Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Statement of Comprehensive Income [Abstract]
Net income	$ 1,048	$ 933
Less: Net income attributable to noncontrolling interests	25	20
Net income attributable to Aon shareholders	1,023	913
Other comprehensive income (loss), net of tax:
Change in fair value of financial instruments	1	11
Foreign currency translation adjustments	(7)	(70)
Postretirement benefit obligation	33	29
Total other comprehensive income (loss)	27	(30)
Less: Other comprehensive income (loss) attributable to noncontrolling interests	(1)	0
Total other comprehensive income (loss) attributable to Aon shareholders	28	(30)
Comprehensive income attributable to Aon shareholders	$ 1,051	$ 883