Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Statement of Comprehensive Income [Abstract]
Net income	$ 514	$ 393	$ 1,562	$ 1,326
Less: Net income attributable to noncontrolling interests	13	14	38	34
Net income attributable to Aon shareholders	501	379	1,524	1,292
Other comprehensive income (loss), net of tax:
Change in fair value of financial instruments	(9)	(1)	(8)	10
Foreign currency translation adjustments	(436)	115	(443)	45
Postretirement benefit obligation	28	33	61	62
Total other comprehensive income (loss)	(417)	147	(390)	117
Less: Other comprehensive loss attributable to noncontrolling interests	0	0	(1)	0
Total other comprehensive income (loss) attributable to Aon shareholders	(417)	147	(389)	117
Comprehensive income attributable to Aon shareholders	$ 84	$ 526	$ 1,135	$ 1,409