|
Employee Benefits (Details 5) (USD $)
In Millions, unless otherwise specified |
Dec. 31, 2011
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Dec. 31, 2010
|
Dec. 31, 2009
|
|---|---|---|---|
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U.S. Pension Plan
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| Fair values of Aon's pension plan assets | |||
| Total | $ 1,325 | $ 1,244 | $ 1,153 |
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U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1)
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| Fair values of Aon's pension plan assets | |||
| Total | 287 | 298 | |
|
U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash and cash equivalents
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 22 | ||
|
U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | Highly liquid debt instruments
|
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| Fair values of Aon's pension plan assets | |||
| Total | 1 | ||
|
U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | Large cap domestic
|
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| Fair values of Aon's pension plan assets | |||
| Total | 151 | 247 | |
|
U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | Large cap international
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| Fair values of Aon's pension plan assets | |||
| Total | 9 | 11 | |
|
U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity derivatives
|
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| Fair values of Aon's pension plan assets | |||
| Total | 63 | ||
|
U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | Real estate and REITS
|
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| Fair values of Aon's pension plan assets | |||
| Total | 42 | 39 | |
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U.S. Pension Plan | Significant Other Observable Inputs (Level 2)
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| Fair values of Aon's pension plan assets | |||
| Total | 847 | 753 | |
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U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | Highly liquid debt instruments
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 26 | ||
|
U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | Large cap international
|
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| Fair values of Aon's pension plan assets | |||
| Total | 88 | ||
|
U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | Equity derivatives
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 110 | 231 | |
|
U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | Small Cap Domestic
|
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| Fair values of Aon's pension plan assets | |||
| Total | 58 | 22 | |
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U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | Corporate bonds
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| Fair values of Aon's pension plan assets | |||
| Total | 355 | 395 | |
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U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | Government and agency bonds
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| Fair values of Aon's pension plan assets | |||
| Total | 116 | 50 | |
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U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | Asset-backed securities
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| Fair values of Aon's pension plan assets | |||
| Total | 18 | 5 | |
|
U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | Fixed income derivatives
|
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| Fair values of Aon's pension plan assets | |||
| Total | 83 | 6 | |
|
U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | Commodity derivatives
|
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| Fair values of Aon's pension plan assets | |||
| Total | 19 | 18 | |
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U.S. Pension Plan | Significant Unobservable (Level 3) Inputs
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| Fair values of Aon's pension plan assets | |||
| Total | 191 | 193 | 138 |
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U.S. Pension Plan | Fair Value | Cash and cash equivalents
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 22 | ||
|
U.S. Pension Plan | Fair Value | Highly liquid debt instruments
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 27 | ||
|
U.S. Pension Plan | Fair Value | Large cap domestic
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 151 | 247 | |
|
U.S. Pension Plan | Fair Value | Large cap international
|
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| Fair values of Aon's pension plan assets | |||
| Total | 97 | 11 | |
|
U.S. Pension Plan | Fair Value | Equity derivatives
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 173 | 231 | |
|
U.S. Pension Plan | Fair Value | Small Cap Domestic
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 58 | 22 | |
|
U.S. Pension Plan | Fair Value | Corporate bonds
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 355 | 395 | |
|
U.S. Pension Plan | Fair Value | Government and agency bonds
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 116 | 50 | |
|
U.S. Pension Plan | Fair Value | Asset-backed securities
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 18 | 5 | |
|
U.S. Pension Plan | Fair Value | Fixed income derivatives
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 83 | 6 | |
|
U.S. Pension Plan | Fair Value | Alternative investments
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 191 | 193 | |
|
U.S. Pension Plan | Fair Value | Commodity derivatives
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 19 | 18 | |
|
U.S. Pension Plan | Fair Value | Real estate and REITS
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 42 | 39 | |
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International Pension Plan
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| Fair values of Aon's pension plan assets | |||
| Total | 5,098 | 4,288 | 3,753 |
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International Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1)
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| Fair values of Aon's pension plan assets | |||
| Total | 1,703 | 175 | |
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International Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash and cash equivalents
|
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| Fair values of Aon's pension plan assets | |||
| Total | 276 | 54 | |
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International Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Equity Securities
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 128 | 121 | |
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International Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed income investments
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 1,299 | ||
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International Pension Plan | Significant Other Observable Inputs (Level 2)
|
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| Fair values of Aon's pension plan assets | |||
| Total | 2,496 | 3,186 | |
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International Pension Plan | Significant Other Observable Inputs (Level 2) | Equity derivatives
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 11 | ||
|
International Pension Plan | Significant Other Observable Inputs (Level 2) | Global
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 960 | 661 | |
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International Pension Plan | Significant Other Observable Inputs (Level 2) | Europe
|
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| Fair values of Aon's pension plan assets | |||
| Total | 347 | 574 | |
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International Pension Plan | Significant Other Observable Inputs (Level 2) | North America
|
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| Fair values of Aon's pension plan assets | |||
| Total | 56 | 133 | |
|
International Pension Plan | Significant Other Observable Inputs (Level 2) | Asia Pacific
|
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| Fair values of Aon's pension plan assets | |||
| Total | 67 | ||
|
International Pension Plan | Significant Other Observable Inputs (Level 2) | Other Equity Securities
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 8 | ||
|
International Pension Plan | Significant Other Observable Inputs (Level 2) | Fixed income investments
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 56 | ||
|
International Pension Plan | Significant Other Observable Inputs (Level 2) | Fixed income derivatives
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 21 | ||
|
International Pension Plan | Significant Other Observable Inputs (Level 2) | Fixed income investments, pooled funds
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 907 | ||
|
International Pension Plan | Significant Other Observable Inputs (Level 2) | Fixed income securities
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 823 | 805 | |
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International Pension Plan | Significant Other Observable Inputs (Level 2) | Derivatives
|
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| Fair values of Aon's pension plan assets | |||
| Total | 178 | (28) | |
|
International Pension Plan | Significant Other Observable Inputs (Level 2) | Commodities
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 26 | 34 | |
|
International Pension Plan | Significant Other Observable Inputs (Level 2) | REITS
|
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| Fair values of Aon's pension plan assets | |||
| Total | 4 | 8 | |
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International Pension Plan | Significant Other Observable Inputs (Level 2) | Alternative investments
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 17 | ||
|
International Pension Plan | Significant Other Observable Inputs (Level 2) | Commodity derivatives
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 14 | ||
|
International Pension Plan | Significant Unobservable (Level 3) Inputs
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 899 | 927 | 746 |
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International Pension Plan | Significant Unobservable (Level 3) Inputs | Global
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 162 | 145 | |
|
International Pension Plan | Significant Unobservable (Level 3) Inputs | Fixed income investments, pooled funds
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 40 | ||
|
International Pension Plan | Significant Unobservable (Level 3) Inputs | Annuities
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 419 | 380 | 432 |
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International Pension Plan | Significant Unobservable (Level 3) Inputs | Real Estate
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 134 | 127 | 136 |
|
International Pension Plan | Significant Unobservable (Level 3) Inputs | Alternative investments
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 346 | 218 | 33 |
|
International Pension Plan | Fair Value
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 4,288 | ||
|
International Pension Plan | Fair Value | Cash and cash equivalents
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 276 | 54 | |
|
International Pension Plan | Fair Value | Equity derivatives
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 11 | ||
|
International Pension Plan | Fair Value | Global
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 960 | 823 | |
|
International Pension Plan | Fair Value | Europe
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 347 | 574 | |
|
International Pension Plan | Fair Value | North America
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 56 | 133 | |
|
International Pension Plan | Fair Value | Asia Pacific
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 67 | ||
|
International Pension Plan | Fair Value | Other Equity Securities
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 128 | 129 | |
|
International Pension Plan | Fair Value | Fixed income investments
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 1,355 | ||
|
International Pension Plan | Fair Value | Fixed income derivatives
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 21 | ||
|
International Pension Plan | Fair Value | Fixed income investments, pooled funds
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 947 | ||
|
International Pension Plan | Fair Value | Fixed income securities
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 823 | 805 | |
|
International Pension Plan | Fair Value | Annuities
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 419 | 380 | |
|
International Pension Plan | Fair Value | Derivatives
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 178 | (28) | |
|
International Pension Plan | Fair Value | Commodities
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 26 | 34 | |
|
International Pension Plan | Fair Value | REITS
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 4 | 8 | |
|
International Pension Plan | Fair Value | Real Estate
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 134 | 127 | |
|
International Pension Plan | Fair Value | Alternative investments
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | 346 | 235 | |
|
International Pension Plan | Fair Value | Commodity derivatives
|
|||
| Fair values of Aon's pension plan assets | |||
| Total | $ 14 |