Condensed Consolidated Statements of Comprehensive Income (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 341us-gaap_ProfitLoss	$ 336us-gaap_ProfitLoss
Less: Net income attributable to noncontrolling interests	13	11
Net income attributable to Aon shareholders	328	325
Other comprehensive (loss) income, net of tax:
Change in fair value of investments	(1)	1
Change in fair value of derivatives	6	9
Foreign currency translation adjustments	(322)	16
Post-retirement benefit obligation	23	26
Total other comprehensive (loss) income	(294)	52
Less: Other comprehensive (loss) income attributable to noncontrolling interests	(1)	(2)
Total other comprehensive (loss) income attributable to Aon shareholders	(293)	54
Comprehensive income attributable to Aon shareholders	$ 35us-gaap_ComprehensiveIncomeNetOfTax	$ 379us-gaap_ComprehensiveIncomeNetOfTax

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

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