In Q2, our global team delivered outstanding results across each of our key financial metrics, and I'd note particular strength across the top and bottom line with 11% organic revenue growth, driven by mid-single-digit or greater organic revenue growth from every solution line, highlighted the particular strength in commercial risk at 14%, which translated into 17% adjusted earnings per share growth in Q2 and 13% free cash flow growth for the first half.
Our 8% organic revenue growth for the first half reflects mid-single-digit or greater organic revenue growth from four of our five solution lines.
Second, the events of the past 16 months have honed the power of Aon United and our ability to work together to deliver new sources of value to clients.
Our colleagues are delivering client retention and net new business generation across all solution lines, driving 8% organic revenue growth over the first half and 11% organic revenue growth this quarter, our strongest performance in almost two decades.
And our Aon Business Services operating platform is digitizing our firm, improving the client experience and enabling efficiency, as demonstrated by operating margin expansion and 13% free cash flow growth in the first half.
We delivered continued progress for both the quarter and year-to-date, including an impressive 11% organic revenue growth in Q2.
As I further reflect on our performance for the first half of the year, as Greg noted, organic revenue growth was 11% in the second quarter and 8% year-to-date.
I would also note the total reported revenue was up 16% in Q2 and 12% year-to-date, including the favorable impact from changes in FX rates, driven by a weaker U.S. dollar versus most currencies.
Our strong revenue growth and ongoing operational discipline contributed to adjusted operating income growth of 11% in Q2 and 14% through the first half of the year.
As we communicated in Q1, the timing of expenses is changing year-over-year such that $135 million of expenses moved into Q2 from Q4.
The $135 million is approximately 1.5% of our total 2020 expense base.
In Q2, this repatterning negatively impacted margins by approximately 470 basis points, resulting in Q2 operating margin contraction of 100 basis points.
Excluding this impact, margins would have expanded by 370 basis points in Q2 and 250 basis points for the first half of 2021.
As we said before, we expected a further $65 million to move from Q4 into Q3 for a total of $200 million of expenses moving out of Q4.
Collectively, the headwind from expense repatterning and tailwind from slower investment as compared to growth were the main factors driving 100 basis points of margin contraction in Q2 and the 40 basis points of margin expansion in the first half of 2021.
We've translated strong operating income growth into adjusted earnings per share growth of 17% in Q2 and 16% year-to-date.
As noted in our earnings material, FX translation was a favorable impact of approximately $0.04 in Q2 and $0.22 year-to-date.
If currency to remain stable at today's rates, we'd expect a $0.02 per share favorable impact to Q3 and $0.01 per share favorable impact in Q4.
In accordance with the business combination agreement, we have paid the $1 billion termination fee to Willis Towers Watson.
As part of the termination, we also expect to incur approximately $350 million to $400 million of additional charge in Q3 related to transaction costs and compensation expenses as well as a small number of actions related to further steps on our Aon United operating model.
Given the outstanding work our colleagues have done over the last past 16 months, we've taken steps internally to ensure our colleagues share in the growth potential of the firm going forward, and this includes those who are previously offered retention bonuses in connection with the combination.
Free cash flow increased 13% year-to-date to $1.3 billion, driven primarily by strong operating income growth and a decline in structural uses of cash.
We continue to expect to drive free cash flow growth over the long term, building on our long-term track record of 14% CAGR over the last 10 years, based on operating income growth, working capital improvements and reduced structural use of cash.
In the second quarter, we repurchased approximately 1.1 million shares for approximately $240 million.
Our financial profile has improved over the past 18 months.
And considering our June 30 balance sheet and the payment of the termination fee, we estimate we have $1.5 billion of additional debt capacity for discretionary use in the second half as we return to historical leverage ratios while maintaining our current investment-grade credit rating.

Summary:
We've translated strong operating income growth into adjusted earnings per share growth of 17% in Q2 and 16% year-to-date.