And lastly, I'll provide an AIG 200 update.
We made meaningful progress on the separation of life retirement from AIG and we significantly advance AIG 200 with the transformation remaining on track to deliver $1 billion in savings by the end of 2022 against the cost to achieve $1.3 billion.
We ended the first quarter with parent liquidity of $7.9 billion and we repurchased $92 million of common stock in connection with warrant exercises and an additional $207 million against the $500 million buyback plan we mentioned on our last call.
We expect to complete the additional $230 million of that buyback plan by the end of the second quarter.
Turning to general insurance, net premiums written increase approximately $600 million year over year, or approximately 6% on an FX constant basis, driven by nearly $1 billion, or a 22% year-over-year increase in our global commercial businesses.
This 22% increase in global commercial was driven by higher retentions; excellent new business production, particularly in international; strong performance in first-quarter portfolio repositioning; and continued rate momentum.
North America commercial net premiums written grew by approximately 29%, an outstanding result due to a variety of factors including increased 1/1 writings on the balance sheet, continue strong submission flow in Lexington, rate improvement, strong retention and higher new business and segments we have been targeting for growth.
The international commercial had an exceptionally strong first quarter with the year-over-year growth in net premiums written of approximately 13% on an FX constant basis.
Looking ahead, we expect overall growth in net premiums written for the remainder of 2021 to be higher than the 6% we saw in the first quarter of this year with more balance in growth across our global commercial and personal portfolios.
With respect to rate, momentum continued with overall global commercial rate increases of 15%.
North America's commercial rate increases were also 15%, driven by improvements in Lexington casualty with 36% rate increases, excess casualty with 31% rate increases, and financial lines with rate increases over 24%.
International commercial rate increases maintain strong momentum at 14%in the first quarter of 2021, which is typically the largest quarter of the year for our European business.
These increases were driven by energy with 26% rate increases, commercial property with 19% rate increases, and financial lines with 20% rate increases.
Turning to global personal insurance, net premiums written in the first quarter declined 23% on an FX constant basis due to our travel business continuing to be impacted by the pandemic as well as reinsurance sessions to Syndicate 2019.
Adjusted for these impacts, global personal insurance, net premiums written were down only 1.6% on an FX constant basis.
In the first quarter of this year, the adjusted accident year combined ratio was 92.4%, a 310-basis-point improvement year over year, driven by a 440-basis-point improvement in our adjusted commercial accident year combined ratio.
The adjusted accident year loss ratio improved 160 basis points, to 59.2%, driven by a 330-basis-point improvement in global commercial.
The expense ratio improved 150 basis points reflecting the impact of AIG 200 savings and continued expense discipline.
We expect to continue to improve the expense ratio throughout 2021, particularly as we deliver on our AIG 200 programs.
To provide further color on combined ratio improvements, in North America, the adjusted accident year combined ratio improved to 95.6%, 210-basis-point improvement year over year.
This reflects a 370-basis-point improvement in the North American commercial lines adjusted accident year combined ratio, which came in at 93.9%.
In international, the adjusted accident year combined ratio improved to 90.2%, a 340-basis-point improvement year over year.
This reflects a 490-basis-point improvement in the international commercial lines adjusted accident year combined ratio, which came in at 86.8%, 150-basis-point improvement in the international personal lines adjusted accident year combined ratio which was 94%.
Net cap losses in general insurance are $422 million primarily driven by the Texas storms and do not include any new COVID-related estimated losses for the first quarter.
As I noted, Validus Re saw strong 1/1 renewals across most lines with attractive levels of risk-adjusted rate improvement.
With respect to April 1 renewals, within the international property, rate adjustments varied from mid-single-digits to upwards of 30% and loss impacted accounts and our Japanese renewals were very successful with 100% client retention, net limits largely similar year over year, and risk-adjusted rate increases, which were in the high single-digits.
Growth limits and global commercial will reduce by over $650 billion.
North America excess casualty removed over $10 billion in mid-limits and increased writings in mid-excess layers in order to achieve a more balanced portfolio.
The portfolio is now more balanced and the submission flow has increased over 100% over the last couple of years.
Adjusted pre-tax income in the first quarter was $941 million, an adjusted return on common equity was 14.2% reflecting our diversified businesses and high-quality investment portfolio.
We continue to actively manage impacts from the low-interest rate and tighter credit spreads environment and the range we previously provided for expected annual spread compression of 8 to 16 basis points has not changed.
With respect to the separation of life retirement from AIG, we continue to work diligently and with a sense of urgency toward an IPO of about 19.9% of the business.
Turning to AIG 200, all 10 operational programs are deep into execution mode.
Recent progress on IT modernization has enabled us to reach the halfway point or $500 million of our run-rate savings target.
$250 million in cumulative run-rate savings has been realized in APTI through the first quarter of this year with $75 million of incremental savings achieved within the first-quarter income statement.
Key highlights on our progress include the successful transition of our shared services operations and over 6,000 colleagues to Accenture at year-end 2020.
And with a new highly experienced leader in Japan, we made significant progress during the first quarter on our AIG 200 strategy in Japan and are on track to finalize target outcomes as we modernize this business by developing digital capabilities with agile product innovation.
Since Peter has already provided a good overview of the quarter, I'll just add that we've posted a 7.4% annualized adjusted return on common equity at the AIG level, an 8.2% adjusted return on tangible common equity at the AIG level, an 8.5% adjusted return on segment common equity for general insurance, and a 14.2% adjusted return on segment common equity for life and retirement.
Now moving to general insurance, first-quarter adjusted pre-tax income was $845 million, up $344 million year over year, primarily reflecting increased underwriting income in international, as well as increased global net investment income driven by alternatives.
Catastrophe losses totaled $422 million pre-tax or 7.3 loss ratio points this quarter, compared to 6.9 loss ratio points in the prior-year quarter.
The CAT losses were mostly comprised of $390 million related to the winter storms, primarily impacting commercial lines including AIG rate.
Overall, prior-year development was $56 million favorable this quarter, which included $58 million of net favorable development in North America, driven by $52 million of favorable development from the ADC amortization, and $2 million of net unfavorable development in international.
It's worthwhile to note that general insurance still has $6.6 billion remaining of the 80% quota share ADC cover.
There was also, embedded within these figures, $33 million of unfavorable development related to COVID-19 claims that relate back to 2020 loss occurrences or a movement of less than 3%, emanating primarily from Validus Re and Talbot or Lloyd's syndicate.
As Peter, noted on a global-commercial-lines basis, the accident year combined ratio, excluding CAT was 90.4%, which represents a 440-basis-point improvement over the prior year's quarter with 75% of that improvement attributable to a lower loss ratio and 25% of the improvement attributable to a lower expense ratio.
Although North American personal lines had a 74% drop in net premiums written as Peter highlighted, it's also important to understand that the other units within the segment which represented nearly 50% of the quarter's net written premium is comprised mostly of warranty and personal A&H business had their net premium only fall marginally.
The increase achieved in the first quarter of 2020 and compounded in the first quarter of 2021 alone, ignoring prior to 2020 rate increases, exceeded 150% for Bermuda-based capacity business, which makes sense given recent years' price deficiency on these capacity excess layers, and approximately 115% for the other mentioned units.
financial lines on the same compound basis has seen in excess of 80% increases for the staples of D&O and EPLI.
Internationally, the 14% first-quarter overall rate increase saw continued rate expansion in key markets, such as the U.K. at plus 23%, global specialty at plus 15%, Europe and the Middle East at 14%, Latin America at 13%, and Asia Pacific also at 13% when excluding the tempering influence of predominantly Japan at 3%.
Lastly cyber achieved our highest rate increase yet at 41% for the quarter.
So, first, our achieved North America commercial rate change for the quarter on a net basis is now estimated to be at least 150 basis points stronger than the corresponding growth rate change, largely due to our increased net positions across selected product lines.
Now, even with superior risk selection rate and term condition changes that have been achieved, renewal retentions have improved to the mid-80% in the aggregate across all commercial lines in both North America and across internationally.
As a result, I would like to reconfirm our outlook for a sub-90% accident year combined ratio excluding CAT by the end of 2022.
Global commercial lines are very nearly at the sub-90% level now and global personal lines is running at 96% for the first quarter.
We are highly confident that we will achieve our sub-90% target and have several pass to help us get there.
North America commercial is expecting to see growth of approximately 10% for the second quarter of 2021 relative to the prior-year quarter, driven mostly from Lexington across a host of product lines and admitted casualty both primary and excess.
You will recall, North American personal had a negative $150 million net written premium in the second quarter of 2020 due to many syndicate 2019 treaties becoming effective, including an unearned premium cover for the PCG high-net-worth book.
So, overall, for North America, both personal and commercial combined, we anticipate net written premium growth between 35% to 40% for the second quarter over the second quarter of the prior year.
International commercial in the second quarter of 2021 is expected to be roughly plus 7% net written premium growth, driven by global specialty, financial lines, and Talbot, and international purpose -- personal is expected to be approximately flat relative to the prior-year quarter.
Now, turning to life and retirement, adjusted pre-tax income increased by 57% or $340 million compared to the first quarter of 2020 with favorable equity markets driving higher private equity returns, lower deferred acquisition and cost amortization, a rebound in most areas of sales, and higher-fee income.
This increase was partially offset by adverse mortality as U.S. COVID-related population death of approximately 205,000 in the first quarter were higher than or earlier anticipated which was also reflected in our own experience.
Individual retirement premium and deposits grew 8% from the prior-year quarter, which we consider a pre-COVID quarter as the sales pipeline carried through March of last year with index and variable annuities, both exceeding prior-year levels.
In group retirement, group acquisition deposits increased significantly from prior year, although both periodic and nonperiodic deposits declined, leading to a marginal reduction in overall gross group premiums and deposits of 2%.
In life insurance, premiums and deposits grew 6% overall with year-over-year growth in both the U.S. and international.
Individual retirement net flows improved by approximately $1 billion over the first quarter of 2020 driven by variable annuities and retail mutual fund.
And yet when excluding retail mutual funds, net flows were positive, led by index annuities rebounding to be plus 1 billion for the quarter, which is virtually identical to one year ago, but with steady progress from a low of 439 million in the second quarter of 2020 to the plus 1 billion this quarter.
Adjusted pre-tax loss was 530 million, which was inclusive of 176 million of losses from the consolidation and eliminations line, which principally reflects adjustments, offsetting investment returns in the subsidiaries by being eliminated in other operations.
Before consolidation and eliminations, adjusted pre-tax loss was $354 million, which was $481 million better than the first quarter of 2020, which included a $317 million adjusted pre-tax loss related to Fortitude and a $30 million one-time cash grant given to employees to help with unanticipated costs when the global pandemic began last March.
Net investment income on an APTI basis was 3.2 billion or 492 million higher than the first quarter of 2020.
Adjusting first-quarter 2020 for Fortitude's investment income to make the comparison apples to apples, this quarter's net investment income on an APTI basis was actually 611 million higher than the prior year, or plus 23%, reflecting strong private equity and real estate returns, as well as bond tender and call premiums, which more than offset the lower income on the AFS fixed income portfolio.
At March 31, book value per common share was $72.37, down 5.3% from year-end, reflecting net unrealized mark-to-market losses on the investment portfolio.
Adjusted book value per share was $58.69, up nearly 3% from December 31.
At quarter-end, AIG parent, as Peter noted, had cash and short-term liquidity assets of $7.9 billion, and we repaid our March debt maturity of $1.5 billion and repurchased the $362 million of shares, as Peter outlined.
Our GAAP debt leverage at March 31 was 28.4%, flat to year-end given downward fixed income market movements negatively impacting AOCI despite the repaid debt maturity mentioned earlier.
For general insurance, we estimate the U.S. pool fleet risk-based capital ratio for the first quarter to be between 465% and 475%, and life and retirement fleet is estimated to be between 435% and 445%, both well above our target ranges.

Summary:
At March 31, book value per common share was $72.37, down 5.3% from year-end, reflecting net unrealized mark-to-market losses on the investment portfolio.