Nick has led many of Oliver Wyman's major practices in his 23 years with the business and I look forward to seeing Oliver Wyman continue to grow and thrive under his leadership.
Our adjusted earnings per share increased by an impressive 33%, and we generated margin expansion despite challenging expense comparisons.
The Marsh Global Insurance Market Index showed price increases of 13% year-over-year versus 18% in the first quarter.
Global property insurance was up 12% and global financial and professional lines were up 34%, driven in part by steep cyber increases, while global casualty rates are up 6% on average and U.S. workers' compensation rates declined modestly in the quarter.
Guy Carpenter's global property catastrophe rate online index increased 6% at midyear.
We generated adjusted earnings per share of $1.75, which is up 33% versus a year ago, driven by strong top line growth and continued low levels of T&E.
Total revenue increased 20% versus a year ago and rose 13% on an underlying basis, the highest quarterly growth in two decades.
Underlying revenue grew 13% in RIS and 12% in consulting.
Marsh grew 14% in the quarter on an underlying basis, the highest quarterly underlying growth in nearly two decades and benefited from stronger business and renewal growth.
Guy Carpenter grew 12% on an underlying basis in the quarter, continuing its string of excellent results.
Mercer underlying revenue grew 6% in the quarter, the highest in almost a decade.
Oliver Wyman posted record reported underlying revenue growth of 28%.
Overall, the second quarter saw adjusted operating income growth of 24%, and our adjusted operating margin expanded 90 basis points year-over-year.
With 9% underlying revenue growth year-to-date, our full year growth will be strong.
Highlights from our second quarter performance included the strongest underlying growth at Marsh since the first quarter of 2003; the strongest at Guy Carpenter in 15 years; solid rebound at 6% at Mercer; and record reported underlying growth at Oliver Wyman.
Consolidated revenue increased 20% in the second quarter to $5 billion, reflecting underlying growth of 13%.
Operating income in the quarter was $1.2 billion, an increase of 39% over the prior year.
Adjusted operating income increased 24% to $1.2 billion, and our adjusted operating margin increased 90 basis points to 26.4%.
GAAP earnings per share was $1.50 in the quarter and adjusted earnings per share increased 33% to $1.75.
For the first six months of 2021, underlying revenue growth was 9%, and adjusted operating income grew 22% to $2.6 billion.
Our adjusted operating margin increased 170 basis points.
Our adjusted earnings per share increased 26% to $3.74.
Second quarter revenue was $3.1 billion, up 21% compared with a year ago or 13% on an underlying basis.
Operating income increased 37% to $950 million.
Adjusted operating income increased 22% to $927 million, and our adjusted operating margin expanded 30 basis points to 32.4%.
For the first six months of the year, revenue was $6.4 billion, with underlying growth of 10%.
Adjusted operating income for the first half of the year increased 19% to $2 billion with a margin of 34.5%, up 110 basis points from the same period a year ago.
At Marsh, revenue in the quarter was $2.7 billion, up 23% compared with a year ago, 14% on an underlying basis.
Even excluding the impact of the revenue adjustment we reported a year ago, underlying revenue at Marsh was up 12%.
The U.S. and Canada region delivered another exceptional quarter with underlying revenue growth of 15%, the highest result since we began reporting this segment.
In international, underlying growth was 13%, EMEA was up 16%, Asia Pacific was up 10% and Latin America grew 2%.
For the first six months of the year, Marsh's revenue was $5 billion, with underlying growth of 11%.
U.S. and Canada underlying growth was 12% and international was up 9%.
Guy Carpenter's second quarter revenue was $488 million, up 13% compared with a year ago or 12% on an underlying basis.
Guy Partner has now achieved 7% or higher underlying growth in six of the last eight quarters.
For the first six months of the year, Guy Carpenter generated $1.4 billion of revenue and 8% underlying growth.
In the Consulting segment, revenue in the quarter was $1.9 billion, up 17% from a year ago or 12% on an underlying basis.
Operating income increased 35% to $344 million.
Adjusted operating income increased 34% to $356 million, and the adjusted operating margin expanded by 220 basis points to 19.5%.
Consulting generated revenue of $3.8 billion for the first six months of 2021, representing underlying growth of 8%.
Adjusted operating income for the first half of the year increased 31% to $726 million.
Mercer's revenue was $1.3 billion in the quarter, up 6% on an underlying basis, representing a meaningful acceleration from the first quarter.
Career grew 15% on an underlying basis, reflecting the rebound in the economy and business confidence.
Wealth increased 4% on an underlying basis, reflecting strong growth in investment management offset by a modest decline in defined benefit.
Our assets under delegated management grew to $393 billion at the end of the second quarter, up 28% year-over-year and 3% sequentially, benefiting from net new inflows and market gains.
Health underlying revenue growth was 4% in the quarter, driven by strength internationally.
Oliver Wyman's revenue in the quarter was $618 million, an increase of 28% on an underlying basis.
For the first six months of the year, revenue at Oliver Widen was $1.2 billion, an increase of 19% on an underlying basis.
Adjusted corporate expense was $62 million in the second quarter.
However, the net benefit credit was $71 million in the quarter.
Investment income was $19 million in the second quarter on a GAAP basis and $18 million on an adjusted basis and mainly reflects gains on our private equity portfolio.
Interest expense in the second quarter was $110 million compared to $132 million in the second quarter of 2020, reflecting lower debt levels in the period.
Based on our current forecast, we expect approximately $110 million of interest expense in the third quarter.
Our adjusted effective tax rate in the second quarter was 24.4% compared with 25% in the second quarter last year.
Excluding discrete items, our effective adjusted tax rate was approximately 25.5%.
Our GAAP tax rate was 31.6% in the second quarter, up from 26.2% in the second quarter of 2020.
The increase reflects a $100 million impact from the revaluation of deferred tax liabilities due to an increase in the U.K. statutory tax rate that goes into effect in 2023.
Through the first half of the year, our adjusted effective tax rate was 24.4% compared with 24% last year.
Based on the current environment, we continue to expect an adjusted effective tax rate between 25% and 26% for 2021, excluding discrete items.
We ended the quarter with $10.8 billion of total debt.
This reflects repayment of $500 million of senior notes in April, which completed our JLT-related deleveraging.
Our next scheduled debt maturity is in January of 2022 when $500 million of senior notes mature.
We continue to expect to deploy approximately $3.5 billion and possibly more capital in 2021, of which at least $3 billion will be deployed across dividends, acquisitions and share repurchases.
Last week, we raised our dividend 15%, which is the largest increase since the third quarter of 1998.
We also repurchased 2.4 million shares of our stock for $322 million in the second quarter.
Our cash position at the end of the second quarter was $888 million.
Uses of cash in the quarter totaled $993 million and included $241 million for dividends, $322 million for share repurchases and $430 million for acquisitions.
For the first six months, uses of cash totaled $1.4 billion and included $478 million for dividend, $434 million for share repurchases and $473 million for acquisitions.

Summary:
We generated adjusted earnings per share of $1.75, which is up 33% versus a year ago, driven by strong top line growth and continued low levels of T&E.
GAAP earnings per share was $1.50 in the quarter and adjusted earnings per share increased 33% to $1.75.