Number Of Credit Facilities

No definition available.

Name:	aon_NumberOfCreditFacilities
Namespace Prefix:	aon_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

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.

+ References

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 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

Reference 2: 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

+ Details

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

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=34725769&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

+ Details

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

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ 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 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- 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.

+ References

No definition available.

+ Details

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

- Definition

Gross amount of debt extinguished.

+ References

No definition available.

+ Details

Name:	us-gaap_ExtinguishmentOfDebtAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.16)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: 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 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 19, 20, 22
-Article 5

+ Details

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

- 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 - Narrative (Details)		3 Months Ended	12 Months Ended
Debt - Narrative (Details)	May. 07, 2014 EUR (€)	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($) credit_facility	Dec. 31, 2014 USD ($)	Dec. 31, 2015 CAD credit_facility	Dec. 31, 2015 EUR (€) credit_facility	Nov. 13, 2015 USD ($)	May. 20, 2015 USD ($)	Feb. 01, 2015 EUR (€)	Aug. 12, 2014 USD ($)	May. 20, 2014 USD ($)
Debt Instrument [Line Items]
Number of credit facilities \| credit_facility			2		2	2
Total debt			$ 5,737,000,000	$ 5,582,000,000
Weighted average commercial paper outstanding			$ 402,000,000	308,000,000
Senior Notes [Member] \| 4.76% Senior Notes due March 2018 (CAD 375M)
Debt Instrument [Line Items]
Debt face value \| CAD					CAD 375,000,000
Interest rate on debt ( in percentage)			4.76%		4.76%	4.76%
Total debt			$ 271,000,000	322,000,000
Senior Notes [Member] \| 5.00% Senior Notes due September 2020
Debt Instrument [Line Items]
Interest rate on debt ( in percentage)			5.00%		5.00%	5.00%
Total debt			$ 599,000,000	599,000,000
Senior Notes [Member] \| 6.25% Senior Notes due September 2040
Debt Instrument [Line Items]
Interest rate on debt ( in percentage)			6.25%		6.25%	6.25%
Total debt			$ 298,000,000	298,000,000
Senior Notes [Member] \| 3.125% Senior Notes due May 2016
Debt Instrument [Line Items]
Debt face value			$ 500,000,000
Interest rate on debt ( in percentage)			3.125%		3.125%	3.125%
Total debt			$ 500,000,000	500,000,000
Senior Notes [Member] \| 4.75% Senior Notes due 2045
Debt Instrument [Line Items]
Debt face value								$ 600,000,000
Interest rate on debt ( in percentage)			4.75%		4.75%	4.75%
Total debt			$ 598,000,000	0
Senior Notes [Member] \| 2.80% Senior Notes due 2021
Debt Instrument [Line Items]
Debt face value							$ 400,000,000
Interest rate on debt ( in percentage)			2.80%		2.80%	2.80%
Total debt			$ 399,000,000	0
Senior Notes [Member] \| 3.50% Senior Notes due September 2015
Debt Instrument [Line Items]
Interest rate on debt ( in percentage)			3.50%		3.50%	3.50%
Total debt			$ 0	599,000,000
Senior Notes [Member] \| 4.60% Senior Notes due June 2044
Debt Instrument [Line Items]
Interest rate on debt ( in percentage)			4.60%		4.60%	4.60%
Total debt			$ 549,000,000	549,000,000
Senior Notes [Member] \| 2.875% Senior Notes due May 2026 (EUR 500M)
Debt Instrument [Line Items]
Debt face value			$ 500,000,000
Interest rate on debt ( in percentage)			2.875%		2.875%	2.875%
Total debt			$ 545,000,000	605,000,000
Senior Notes [Member] \| 8.205% Junior Subordinated Notes due January 2027
Debt Instrument [Line Items]
Interest rate on debt ( in percentage)			8.205%		8.205%	8.205%
Total debt			$ 521,000,000	521,000,000
Unsecured Debt [Member] \| 4.76% Senior Notes due March 2018 (CAD 375M)
Debt Instrument [Line Items]
Interest rate on debt ( in percentage)			4.76%		4.76%	4.76%
Junior Subordinated Debt [Member] \| 8.205% Junior Subordinated Notes due January 2027
Debt Instrument [Line Items]
Interest rate on debt ( in percentage)			8.205%		8.205%	8.205%
Commercial Paper [Member]
Debt Instrument [Line Items]
Total debt			$ 50,000,000	$ 168,000,000
Weighted-average interest rates (in percentage)			0.50%	0.35%
Notes Payable [Member]
Debt Instrument [Line Items]
Total debt			$ 16,000,000	$ 31,000,000
Notes Payable [Member] \| 3.50% notes due 2024 [Member]
Debt Instrument [Line Items]
Debt face value										$ 350,000,000	$ 250,000,000
Interest rate on debt ( in percentage)										3.50%	3.50%
Notes Payable [Member] \| 4.60% Senior Notes due June 2044
Debt Instrument [Line Items]
Debt face value											$ 550,000,000
Interest rate on debt ( in percentage)											4.60%
Notes Payable [Member] \| 2.875% Senior Notes due May 2026 (EUR 500M)
Debt Instrument [Line Items]
Debt face value \| €	€ 500,000,000
Interest rate on debt ( in percentage)	2.875%
Senior Notes [Member] \| 3.50% Senior Notes due September 2015
Debt Instrument [Line Items]
Interest rate on debt ( in percentage)		3.50%
Extinguishment of debt		$ 600,000,000
Notes Payable [Member] \| 6.25% EUR 500 debt securities due July 2014 [Member]
Debt Instrument [Line Items]
Interest rate on debt ( in percentage)	6.25%
Extinguishment of debt \| €	€ 500,000,000
Credit Facility Expiring March 2017 [Member] \| Line of Credit [Member]
Debt Instrument [Line Items]
New credit and loan facility			400,000,000
Commercial Paper [Member] \| Line of Credit [Member]
Debt Instrument [Line Items]
Long-term commercial paper			50,000,000	$ 168,000,000
European Credit Facility [Member] \| Line of Credit [Member]
Debt Instrument [Line Items]
New credit and loan facility \| €									€ 650,000,000
Credit Facility Expiring February 2020 [Member] \| Line of Credit [Member]
Debt Instrument [Line Items]
New credit and loan facility			900,000,000
Commercial Paper [Member] \| US Commercial Paper Program [Member]
Debt Instrument [Line Items]
New credit and loan facility			$ 900,000,000
Commercial Paper [Member] \| European Multi-Currency Commercial Paper Program [Member]
Debt Instrument [Line Items]
New credit and loan facility \| €						€ 300,000,000