Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 778	$ 308	$ 1,083	$ 645
Less: Net income attributable to noncontrolling interests	9	8	23	20
Net income attributable to Aon shareholders	769	300	1,060	625
Other comprehensive income (loss), net of tax:
Change in fair value of financial instruments	4	(4)	2	(11)
Foreign currency translation adjustments	44	(59)	191	(138)
Postretirement benefit obligation	20	51	38	(150)
Total other comprehensive income (loss)	68	(12)	231	(299)
Less: Other comprehensive income attributable to noncontrolling interests	(5)	0	(4)	0
Total other comprehensive income (loss) attributable to Aon shareholders	73	(12)	235	(299)
Comprehensive income (loss) attributable to Aon shareholders	$ 842	$ 288	$ 1,295	$ 326