Condensed Consolidated Statements of Comprehensive Income (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 315	$ 264	$ 964	$ 788
Less: Net income attributable to noncontrolling interests	6	8	26	30
Net income attributable to Aon shareholders	309	256	938	758
Other comprehensive (loss) income, net of tax:
Change in fair value of investments	0	(14)	(1)	(1)
Change in fair value of derivatives	(8)	9	13	(12)
Foreign currency translation adjustments	(318)	155	(228)	(77)
Post-retirement benefit obligation	26	24	70	65
Total other comprehensive (loss) income	(300)	174	(146)	(25)
Less: Other comprehensive income (loss) attributable to noncontrolling interests	0	3	(2)	1
Total other comprehensive (loss) income attributable to Aon shareholders	(300)	171	(144)	(26)
Comprehensive income attributable to Aon shareholders	$ 9	$ 427	$ 794	$ 732