Other Financial Data - Schedule of Other Non-current Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Other Financial Data [Abstract]
Taxes payable	$ 260	$ 223
Deferred revenue	151	159
Leases	172	166
Compensation and benefits	59	59
Other	125	162
Total	$ 767	$ 769

Employee-related Liabilities, Noncurrent

No definition available.

Name:	aon_EmployeerelatedLiabilitiesNoncurrent
Namespace Prefix:	aon_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Other Financial Data [Abstract]

+ References

No definition available.

+ Details

Name:	aon_OtherFinancialDataAbstract
Namespace Prefix:	aon_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Carrying amount as of the balance sheet date of the unpaid sum of the known and estimated amounts payable to satisfy all domestic and foreign income tax obligations due beyond one year or the operating cycle, whichever is longer. Alternate captions include income taxes payable, noncurrent.

+ 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 210.5-02.24)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 15
-Subparagraph b(1)
-Article 7

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 15
-Article 9

+ Details

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

- Definition

Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal, through the balance sheet date and due to be paid more than one year (or one operating cycle, if longer) after the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6455398&loc=d3e45280-112737

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6455314&loc=d3e45023-112735

Reference 3: 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)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

Total carrying amount of consideration received or receivable as of the balance sheet date representing potential earnings that were not as yet recognized as revenue or other forms of income in conformity with GAAP, and which are expected to be recognized as such after one year or beyond the normal operating cycle, if longer.

+ 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 210.5-02.26)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 605
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 13.A.Q4)
-URI http://asc.fasb.org/extlink&oid=27012821&loc=d3e214044-122780

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 13
-Section A

+ Details

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

- Definition

The noncurrent portion (due beyond one year or one operating cycle) of other accrued expenses (expenses incurred at the end of the reporting period but not yet paid) not otherwise defined in the taxonomy.

+ References

+ Details

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

- Definition

Aggregate carrying amount, as of the balance sheet date, of noncurrent obligations not separately disclosed in the balance sheet. Noncurrent liabilities are expected to be paid after one year (or the normal operating cycle, if longer).

+ References

+ Details

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