Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 418	$ (891)	$ 1,980	$ 435
Less: Net income attributable to noncontrolling interests	10	9	48	43
Net income (loss) attributable to Aon shareholders	408	(900)	1,932	392
Other comprehensive income (loss), net of tax:
Change in fair value of financial instruments	(8)	(5)	(16)	5
Foreign currency translation adjustments	(676)	(153)	(1,119)	(108)
Postretirement benefit obligation	26	25	87	87
Total other comprehensive loss	(658)	(133)	(1,048)	(16)
Less: Other comprehensive income attributable to noncontrolling interests	1	0	0	0
Total other comprehensive loss attributable to Aon shareholders	(659)	(133)	(1,048)	(16)
Comprehensive income (loss) attributable to Aon shareholders	$ (251)	$ (1,033)	$ 884	$ 376