Stockholders' Equity (Details 3) (USD $) In Millions	3 Months Ended	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Comprehensive income (loss), net of related tax:
Net change in derivative (losses) gains	$ (9)	$ 2	$ (14)	$ (24)
Net foreign currency translation adjustments	(209)	207	(12)	(66)
Net post-retirement benefit obligation	(15)	(13)	(42)	(68)
Total other comprehensive (loss) income	(203)	222	16	(22)
Less: other comprehensive (loss) income attributable to noncontrolling interests	(1)	5	(1)	16
Other Comprehensive (loss) income attributable to Aon stockholders	$ (202)	$ 217	$ 17	$ (38)

Total other comprehensive income, after tax.

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The change in equity [net assets] of a business enterprise during a period from transactions and other events and circumstances from non-owner sources which are attributable to the reporting entity. It includes all changes in equity during a period except those resulting from investments by owners and distributions to owners, but excludes any and all transactions which are directly or indirectly attributable to that ownership interest in subsidiary equity which is not attributable to the parent.

+ References

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-Publisher AICPA

-Name Accounting Research Bulletin (ARB)

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-Appendix A

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The change in equity [net assets] of a business enterprise during a period from transactions and other events and circumstances from non-owner sources which are attributable to noncontrolling interests, if any. It includes all changes in equity during a period except those resulting from investments by owners and distributions to owners, which are directly or indirectly attributable to that ownership interest in subsidiary equity which is not attributable to the parent.

+ References

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-Publisher AICPA

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Net changes to accumulated comprehensive income during the period related to benefit plans, after tax, attributable to the parent entity.

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Adjustment that results from the process of translating subsidiary financial statements and foreign equity investments into functional currency of the reporting entity, net of tax.

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Change in accumulated gains and losses from derivative instrument designated and qualifying as the effective portion of cash flow hedges, net of tax effect. The after tax effect change includes an entity's share of an equity investee's increase (decrease) in deferred hedging gains or losses.

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