Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Statement of Comprehensive Income [Abstract]
Net income	$ 467	$ 418	$ 2,121	$ 1,980
Less: Net income attributable to noncontrolling interests	11	10	55	48
Net income attributable to Aon shareholders	456	408	2,066	1,932
Other comprehensive income, net of tax:
Change in fair value of financial instruments	(5)	(8)	6	(16)
Foreign currency translation adjustments	(257)	(676)	(29)	(1,119)
Postretirement benefit obligation	20	26	66	87
Total other comprehensive income (loss)	(242)	(658)	43	(1,048)
Less: Other comprehensive income (loss) attributable to noncontrolling interests	(1)	1	(1)	0
Total other comprehensive income (loss) attributable to Aon shareholders	(241)	(659)	44	(1,048)
Comprehensive income (loss) attributable to Aon shareholders	$ 215	$ (251)	$ 2,110	$ 884