Now, turning to net income for the quarter. We reported a net loss available to common stockholders of $1.2 billion or $7.35 per diluted share. The difference between net and adjusted operating income for the quarter was predominantly driven by two factors. First, there was an unfavorable noneconomic impact within nonoperating income, driven by the negative movement in market risk benefits as the impact of lower interest rates more than offset the benefits from higher equity markets. Of note, we remain pleased with the performance of our VA hedge program. The performance of the program throughout 2023 as the block well positioned for the year ahead. Second, there was a change in the fair value of the GAAP embedded derivative related to the Fortitude Re reinsurance transaction with the corresponding offset to this change flowing through AOCI.
So, now let’s turn to the segment results, starting with Group Protection. Group reported operating income of $52 million compared to $26 million in the prior year quarter. The progress was broad-based as both disability and life loss ratios showed improvement compared to the prior year quarter. And while fourth quarter earnings tend to be lower due to seasonality. Excluding the impacts of the assumption review, results increased $8 million sequentially as improved life mortality more than offset the seasonal headwinds. For the fourth quarter, the Group life loss ratio was 67%, decreasing over 7 percentage points versus the prior year quarter and roughly 10 percentage points sequentially. The improvement was driven by declining severity from the elevated levels experienced in the third quarter.
For disability, the loss ratio was 83%, decreasing by 260 basis points versus the prior year quarter driven by fewer LTD claims incurred. Sequentially, excluding the impacts of the assumption review, the disability loss ratio increased over 7 percentage points reflecting higher claim severity and seasonal trends we’ve experienced in the past. Now, briefly touching on full year results. Excluding assumption reviews, Group reported full year operating income of $275 million and a margin of 5.5% compared to $53 million and a margin of roughly 1% in 2022. The improvement reflected continued progress in our margin expansion efforts through the execution of our strategy, including diversifying our book of business across market segments and products, maintaining pricing discipline on new and renewing business, and operational investments we have made to support claimants in their return to work journey.
As we look towards 2024, the group business will continue to drive growth in both our operating earnings and free cash flow. As I noted last quarter, we remain focused on achieving a sustainable margin of 7%. And as we progress towards that goal, we would expect continued execution of our strategy to drive another 50 to 100 basis points of margin expansion in 2024. Turning to Annuities. Annuities reported operating income of $279 million, which, as I noted earlier, includes a one-time favorable impact of $14 million from model refinement compared to $275 million in the prior year quarter. Excluding the one-time impact, the decrease was primarily due to higher expenses. Sequentially, excluding the impacts of the assumption review and the one-time item, results improved by approximately $5 million, primarily due to improvements in spread income, partially offset by lower average account balances.
However, ending account balances were up 4% for the same period, which will be a tailwind for first quarter results. As we look to 2024, we expect the spread improvement we experienced in the fourth quarter to continue throughout the year and the Annuities business to remain a key driver of earnings and free cash flow for the company. Now, shifting to Retirement Plan Services. Retirement reported operating income of $38 million compared to $52 million in the prior year quarter. For the full year, earnings were $171 million compared to $211 million in the prior year. The declines were primarily driven by higher expenses and participant-driven stable value outflows, resulting from higher interest rates throughout 2023. Average account balances for the quarter increased 9% versus the prior year quarter and end-of-period account balances were over $100 billion for the first time, driven by strength in the equity markets and a ninth consecutive year of positive net flows.
Lastly, turning to Life Insurance. Life reported an operating loss of $6 million compared to an operating loss of $9 million in the prior year quarter, with the run rate impacts from both the Fortitude transaction and our annual assumption review, being offset by an improvement in alternative investment income. Of note, the impact from the Fortitude transaction this quarter was approximately $15 million, slightly less than the expected quarterly run rate of $25 million due to the timing of the close of the transaction. At the same time, we experienced slightly higher mortality severity in the quarter, largely offsetting the favorable impact in the quarter from the timing of the close of the transaction. Sequentially, excluding the impacts of the assumption review and one-time items, earnings declined by $29 million, driven primarily by higher expenses and the run rate impacts from the Fortitude transaction.
Taking a step back, as I previously highlighted, there are a number of headwinds facing the life business, but we continue to expect some of these to lessen over the next few years. In 2024, we anticipate the life business to have modestly positive earnings, driven in part by lower expenses, improving spreads, and higher alternative investment income. We view the actions that we took in 2023 to be foundational to our efforts to deliver earnings growth in this business over time with continued progress being made in 2024. Moving to investments. Following the close of the reinsurance transaction, our total invested assets decreased $28 billion. The portfolio shift is in line with our investment strategy of maintaining both a high-quality and well-diversified portfolio.
The portfolio remains 97% investment grade, with an average credit rating of A. Credit performance was solid during the quarter with negligible credit-related losses. Additional details on our investment portfolio can be found on Pages 14 and 15 in our outlook for presentations. Now, briefly turning to an update on our commercial mortgage loan portfolio. The portfolio continues to be conservatively positioned and performed extremely well. Throughout 2023, we had no material loan modifications or losses, no delinquencies, and no forced extensions. Within our office portfolio, we have future maturities of $133 million and $178 million coming due in 2024 and 2025, respectively, which represents less than 2% of our commercial mortgage loan portfolio.
The near-term maturing office loans continue to perform well and are conservatively positioned with an average debt-to-service coverage ratio of 3.5 times. Lastly, on alternative investment performance. As mentioned previously, alternative investments generated an annualized return of 7% this quarter and for the full year delivered an 8% return. Our alternatives portfolio continues to benefit from our diversified investment approach, delivering strong risk-adjusted long-term returns. I will turn to the outlook in a moment, but first, I want to highlight the information that we’ve provided today. The outlook presentation posted on our website is intended to address three areas of focus. First, as Ellen referred to, is more detail on our strategic priority for the company.
Second, we have laid out a number of guideposts around fundamental financial metrics for the company and our businesses. We recognize the importance of increased disclosures and metrics and we view today as a solid step in that direction. However, this is a starting point as we progress along our journey to reposition our business. Third, in the appendix, we provide an outlook for adjusted operating earnings for 2024. We felt it was necessary to provide a grounding for both the full year ranges of outcomes for the businesses and some of the quarterly seasonality to level set after the Fortitude transaction and its impact on our financial statements. Given the time allotment today, our intention is not to go through every slide, but to hit the major highlights.
Turning to the outlook itself, there are three main points. The first is that we see substantial opportunity to continue to transform Lincoln. Our foundation is one built upon at-scale retail and workplace businesses with leading distribution and a large strength in the balance sheet. The opportunity, however, is to leverage those competitive advantages to evolve our business into one characterized by more stable cash flows, foundational capital strength and a focus on maximizing risk-adjusted returns. And doing this will require us to first, hold more capital than we have previously; second, further optimize our operating model; and third, grow profitably, which for us entails increasing the size and scale of our group business expanding our spread and spread-like products inside our retail businesses, and generally decreasing our sensitivity to equity markets.
Our ability to execute will require strategic financial and operational initiatives many of which we began in the last year. In the outlook presentation, we provide examples of these initiatives, along with an illustrative timeline as can be seen on Page 8. We felt it was important to show the timeline to help you understand the journey we’re on. and to also provide context for the growth in our free cash flow over the next few years rather than simply focusing on 2024 as a number of these initiatives will have one-time costs or some inherent uncertainty around timing. For example, last quarter, I discussed the expense headwinds we are facing and the opportunity to continue rightsizing our expense base. Earlier this week, we took action to remove organizational complexity.
