Condensed Consolidated Statements of Comprehensive Income (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 313	$ 252	$ 649	$ 524
Less: Net income attributable to noncontrolling interests	9	11	20	22
Net income attributable to Aon shareholders	304	241	629	502
Other comprehensive income (loss), net of tax:
Change in fair value of investments	(2)	13	(1)	13
Change in fair value of derivatives	12	(7)	21	(21)
Foreign currency translation adjustments	74	(58)	90	(232)
Post-retirement benefit obligation	18	18	44	41
Total other comprehensive income (loss)	102	(34)	154	(199)
Less: Other comprehensive loss attributable to noncontrolling interests	0	(2)	(2)	(2)
Total other comprehensive income (loss) attributable to Aon shareholders	102	(32)	156	(197)
Comprehensive income attributable to Aon shareholders	$ 406	$ 209	$ 785	$ 305