Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 188	$ 313	$ 529	$ 649
Less: Net income attributable to noncontrolling interests	10	9	23	20
Net income attributable to Aon shareholders	178	304	506	629
Other comprehensive (loss) income, net of tax:
Change in fair value of financial instruments	(6)	10	(1)	20
Foreign currency translation adjustments	175	74	(147)	90
Post-retirement benefit obligation	21	18	44	44
Total other comprehensive (loss) income	190	102	(104)	154
Less: Other comprehensive (loss) income attributable to noncontrolling interests	(1)	0	(2)	(2)
Total other comprehensive (loss) income attributable to Aon shareholders	191	102	(102)	156
Comprehensive income attributable to Aon shareholders	$ 369	$ 406	$ 404	$ 785