Condensed Consolidated Statements of Comprehensive Income (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 336	$ 272
Less: Net income attributable to noncontrolling interests	11	11
Net income attributable to Aon shareholders	325	261
Other comprehensive income (loss), net of tax:
Change in fair value of investments	1	0
Change in fair value of derivatives	9	(14)
Foreign currency translation adjustments	16	(174)
Post-retirement benefit obligation	26	23
Total other comprehensive income (loss)	52	(165)
Less: Other comprehensive income attributable to noncontrolling interests	(2)	0
Total other comprehensive income (loss) attributable to Aon shareholders	54	(165)
Comprehensive income attributable to Aon shareholders	$ 379	$ 96