v2.3.0.15

Cash and Cash Equivalents (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2011 year month segment entity plan	Dec. 31, 2010
Cash and Cash Equivalents.
Cash and cash equivalents, maximum maturity period (in months)	3
Cash and cash equivalents, restricted	$ 183	$ 60
Restricted balances due to a requirement of the Financial Services Authority	$ 123

X

- Details

Name:	aon_CashAndCashEquivalentsDisclosureAbstract
Namespace Prefix:	aon
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Represents the maximum maturity period of cash and cash equivalents, which include cash balances and all highly liquid investments.

+ Details

Name:	aon_CashAndCashEquivalentsMaximumMaturityPeriod
Namespace Prefix:	aon
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Represents the amounts of cash and cash equivalent items which are restricted as to withdrawal or usage due to requirements of the Financial Services Authority.

+ Details

Name:	aon_RestrictedCashAndCashEquivalentRestrictionsImposedByFinancialServicesAuthority
Namespace Prefix:	aon
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

The carrying amounts of cash and cash equivalent items which are restricted as to withdrawal or usage. Restrictions may include legally restricted deposits held as compensating balances against short-term borrowing arrangements, contracts entered into with others, or entity statements of intention with regard to particular deposits; however, time deposits and short-term certificates of deposit are not generally included in legally restricted deposits. Excludes compensating balance arrangements that are not agreements which legally restrict the use of cash amounts shown on the balance sheet. For a classified balance sheet represents the current portion only (the noncurrent portion has a separate concept); there is a separate and distinct element for unclassified presentations.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 1

-Article 5



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

-Publisher AICPA

-Name Audit and Accounting Guide (AAG)

-Number AAG-BRD

-Chapter 4

-Paragraph 80

-Subparagraph Exhibit 4-8, 3

-IssueDate 2006-05-01

+ Details

Name:	us-gaap_RestrictedCashAndCashEquivalentsAtCarryingValue
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant