Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 303	$ 315	$ 832	$ 964
Less: Net income attributable to noncontrolling interests	8	6	31	26
Net income attributable to Aon shareholders	295	309	801	938
Other comprehensive (loss) income, net of tax:
Change in fair value of financial instruments	(10)	(8)	(11)	12
Foreign currency translation adjustments	(229)	(318)	(376)	(228)
Post-retirement benefit obligation	18	26	62	70
Total other comprehensive (loss)	(221)	(300)	(325)	(146)
Less: Other comprehensive (loss) income attributable to noncontrolling interests	(4)	0	(6)	(2)
Total other comprehensive (loss) attributable to Aon shareholders	(217)	(300)	(319)	(144)
Comprehensive income attributable to Aon shareholders	$ 78	$ 9	$ 482	$ 794