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Acquisitions and Dispositions (Details 2) (USD $)
Share data in Millions, except Per Share data, unless otherwise specified |
1 Months Ended | 12 Months Ended | 1 Months Ended | 1 Months Ended | 3 Months Ended | 1 Months Ended | 1 Months Ended | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
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Dec. 31, 2011
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Dec. 31, 2010
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Oct. 31, 2010
Cash Electing Consideration
D
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Oct. 31, 2010
Stock Electing Consideration
D
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Oct. 31, 2010
Hewitt Associates, Inc (Hewitt)
Y
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Dec. 31, 2011
Hewitt Associates, Inc (Hewitt)
|
Dec. 31, 2010
Hewitt Associates, Inc (Hewitt)
|
Oct. 02, 2010
Hewitt Associates, Inc (Hewitt)
|
Dec. 31, 2011
Hewitt Associates, Inc (Hewitt)
HR Solutions
|
Dec. 31, 2010
Hewitt Associates, Inc (Hewitt)
HR Solutions
|
Oct. 30, 2010
Hewitt Associates, Inc (Hewitt)
Cash Electing Consideration
|
Oct. 02, 2010
Hewitt Associates, Inc (Hewitt)
Cash Electing Consideration
|
Oct. 31, 2010
Hewitt Associates, Inc (Hewitt)
Mixed Consideration and Stock Electing Consideration
|
Sep. 30, 2010
Hewitt Associates, Inc (Hewitt)
Mixed Consideration and Stock Electing Consideration
|
Oct. 02, 2010
Hewitt Associates, Inc (Hewitt)
Mixed Consideration and Stock Electing Consideration
|
Oct. 30, 2010
Hewitt Associates, Inc (Hewitt)
Mixed Consideration Election
|
Oct. 02, 2010
Hewitt Associates, Inc (Hewitt)
Mixed Consideration Election
|
Oct. 30, 2010
Hewitt Associates, Inc (Hewitt)
Stock Electing Consideration
|
Oct. 02, 2010
Hewitt Associates, Inc (Hewitt)
Stock Electing Consideration
|
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| Business Acquisition | |||||||||||||||||||
| Percentage of aggregate consideration to be paid in cash and in number of shares each | 50.00% | ||||||||||||||||||
| Par value of Hewitt Class A Common Stock per share (in dollars per share) | $ 0.01 | ||||||||||||||||||
| Common stock, par value (in dollars per share) | $ 1 | $ 1 | $ 1.00 | ||||||||||||||||
| Consecutive trading days | 10 | 10 | |||||||||||||||||
| Closing volume-weighted average price of Aon's common stock (in dollars per share) | $ 39.0545 | $ 39.0545 | |||||||||||||||||
| Cash consideration | |||||||||||||||||||
| Number of Hewitt common shares outstanding electing consideration | 7.78 | 44.52 | 43.67 | ||||||||||||||||
| Cash consideration per common share outstanding (in dollars per share) | $ 50.46 | $ 25.61 | $ 21.19 | ||||||||||||||||
| Cash paid in business acquisition | $ 2,458,000,000 | $ 393,000,000 | $ 1,140,000,000 | $ 925,000,000 | |||||||||||||||
| Stock consideration | |||||||||||||||||||
| Number of Hewitt common shares outstanding electing consideration | 7.78 | 44.52 | 43.67 | ||||||||||||||||
| Exchange ratio of Aon shares issued to Hewitt shareholders (as a percent) | 63.62% | 74.94% | |||||||||||||||||
| Number of Aon common shares issued to finance Hewitt acquisition (in shares) | 61.05 | 61.05 | 28.32 | 32.73 | |||||||||||||||
| Aon's closing common share price (in dollars per share) | $ 39.28 | ||||||||||||||||||
| Total fair value of stock consideration | 2,398,000,000 | ||||||||||||||||||
| Fair value of Hewitt stock options converted to options to acquire Aon common stock | 76,000,000 | ||||||||||||||||||
| Total consideration transferred | 103,000,000 | 5,089,000,000 | 4,932,000,000 | ||||||||||||||||
| Acquisition, integration and financing expenses | 47,000,000 | 54,000,000 | 47,000,000 | 19,000,000 | |||||||||||||||
| Acquisition, integration and financing cost recorded in Other General Expenses | 47,000,000 | 40,000,000 | |||||||||||||||||
| Acquisition, integration and financing cost recorded in interest Expenses | 14,000,000 | ||||||||||||||||||
| Debt Financing of the Transaction | |||||||||||||||||||
| Drawing under Term Loan Credit Facility | 1,000,000,000 | ||||||||||||||||||
| Term of Term Loan Facility (in years) | 3 | ||||||||||||||||||
| Issuance of Notes | $ 1,500,000,000 | ||||||||||||||||||
| Options issued as consideration to former holders of Hewitt stock options (in options) | 4.5 | ||||||||||||||||||