Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 327	$ 341
Less: Net income attributable to noncontrolling interests	12	13
Net income attributable to Aon shareholders	315	328
Other comprehensive (loss) income, net of tax:
Change in fair value of financial instruments	(7)	5
Foreign currency translation adjustments	(79)	(322)
Post-retirement benefit obligation	(201)	23
Total other comprehensive (loss)	(287)	(294)
Less: Other comprehensive (loss) income attributable to noncontrolling interests	0	(1)
Total other comprehensive (loss) attributable to Aon shareholders	(287)	(293)
Comprehensive income attributable to Aon shareholders	$ 28	$ 35