Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 280	$ 188	$ 607	$ 529
Less: Net income attributable to noncontrolling interests	8	10	20	23
Net income attributable to Aon shareholders	272	178	587	506
Other comprehensive (loss) income, net of tax:
Change in fair value of financial instruments	(4)	(6)	(11)	(1)
Foreign currency translation adjustments	(59)	175	(138)	(147)
Post-retirement benefit obligation	51	21	(150)	44
Total other comprehensive (loss) income	(12)	190	(299)	(104)
Other Comprehensive Income (Loss), Net of Tax	(12)	190	(299)	(104)
Less: Other comprehensive loss attributable to noncontrolling interests	0	(1)	0	(2)
Total other comprehensive (loss) income attributable to Aon shareholders	(12)	191	(299)	(102)
Comprehensive income attributable to Aon shareholders	$ 260	$ 369	$ 288	$ 404