Reflects the calculation as of the balance sheet date of the average interest rate weighted by the average outstanding amount of short-term debt outstanding by type or by instrument at that time.

No definition available.

+ Details

Name:	aon_ShortTermDebtAverageOutstandingAmountWeightedAverageInterestRate
Namespace Prefix:	aon_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Sum of the carrying values as of the balance sheet date of all debt, including all short-term borrowings, long-term debt, and capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.16)

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.13,16)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

Name:	us-gaap_DebtAndCapitalLeaseObligations
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

For the form of debt having an initial term of less than one year or less than the normal operating cycle, if longer, average borrowings during the period.

+ References

No definition available.

+ Details

Name:	us-gaap_ShorttermDebtAverageOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Debt (Details)	3 Months Ended
Debt (Details)	Mar. 31, 2015 Commercial paper [Member] USD ($)	Dec. 31, 2014 Commercial paper [Member] USD ($)	Dec. 31, 2014 Domestic Line of Credit [Member] 2017 Facility [Member] Line of Credit [Member] USD ($)	Mar. 31, 2015 Foreign Line of Credit [Member] 2015 Facility [Member] Line of Credit [Member] USD ($)	Dec. 31, 2014 Foreign Line of Credit [Member] 2015 Facility [Member] Line of Credit [Member] EUR (€)	Feb. 02, 2015 Foreign Line of Credit [Member] 2020 Facility [Member] Line of Credit [Member] USD ($)	Mar. 31, 2015 Commercial paper [Member] US Commercial Paper Program [Member] USD ($)	Mar. 31, 2015 Commercial paper [Member] European Multi Currency Paper Program [Member] EUR (€)
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity			$ 400,000,000	$ 707,000,000	€ 650,000,000	$ 900,000,000	$ 900,000,000	€ 300,000,000
Total debt	355,000,000	168,000,000
Weighted average commercial paper outstanding	$ 317,000,000
Weighted-average interest rates (as a percent)	0.50%