v2.3.0.15

Debt (Details) In Millions, unless otherwise specified | 9 Months Ended |  |  |  |  | 9 Months Ended |  |  | 1 Months Ended |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Sep. 30, 2011 USD ($) | Sep. 30, 2011 Commercial paper USD ($) | May 24, 2011 3.125% Senior notes due 2016 USD ($) | Sep. 30, 2011 Term Loan Facility due 2013 | Jun. 15, 2011 Term Loan Facility due 2013 USD ($) | Sep. 30, 2011 Term Loan Credit Facility USD ($) year | Sep. 30, 2011 4.76% CAD 375 senior unsecured debt securities due March 2018 USD ($) | Mar. 08, 2011 4.76% CAD 375 senior unsecured debt securities due March 2018 CAD | Apr. 30, 2011 5.05% CAD 375 debt securities due April 2011 CAD | Apr. 12, 2011 5.05% CAD 375 debt securities due April 2011
Debt Instrument |  |  |  |  |  |  |  |  |  |
Debt face value |  | $ 100 | $ 500 |  | $ 450 |  | $ 363 | 375 |  |
Interest rate on debt (as a percent) |  |  | 3.125% |  |  |  |  | 4.76% |  | 5.05%
Debt instrument base interest rate |  |  |  | LIBOR |  |  |  |  |  |
Annualized interest rate including LIBOR (as a percent) |  |  |  | 1.56% |  |  |  |  |  |
Term of credit facility (in years) |  |  |  |  |  | 3 |  |  |  |
Debt repayment |  |  |  |  |  | 1,000 |  |  | 375 |
(Loss) gain on extinguishment of debt | $ (19) |  |  |  |  | $ 19 |  |  |  |

X
- Definition Reflects as of the balance sheet date the actual annualized interest rate that includes both LIBOR and the contractual variable rate margin. + Details
Name: | aon_DebtAnnualizedInterestRate
Namespace Prefix: | aon
Data Type: | us-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR. + Details
Name: | aon_DebtInstrumentDescriptionOfVariableRateBasis
Namespace Prefix: | aon
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | instant

X
- Definition Term length of line-of-credit facility. + Details
Name: | aon_LineOfCreditFacilityTerm
Namespace Prefix: | aon
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Decrease for amounts repaid on the debt instrument for the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 08 -Paragraph f -Article 4 + Details
Name: | us-gaap_DebtInstrumentDecreaseRepayments
Namespace Prefix: | us-gaap
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The stated principal amount of the debt instrument at time of issuance, which may vary from the carrying amount because of unamortized premium or discount. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 21 -Paragraph 16, 20 + Details
Name: | us-gaap_DebtInstrumentFaceAmount
Namespace Prefix: | us-gaap
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Interest rate stated in the contractual debt agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22 -Article 5 + Details
Name: | us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix: | us-gaap
Data Type: | us-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + Details
Name: | us-gaap_DebtInstrumentLineItems
Namespace Prefix: | us-gaap
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount represents the difference between the fair value of the payments made and the carrying amount of the debt at the time of its extinguishment. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 26 -Paragraph 20, 21 + Details
Name: | us-gaap_GainsLossesOnExtinguishmentOfDebt
Namespace Prefix: | us-gaap
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration