Condensed Consolidated Statements of Income (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Revenue
Total revenue	$ 2,702	$ 2,385	$ 9,113	$ 8,101
Expenses
Compensation and benefits	1,835	1,387	5,182	4,270
Information technology	130	107	359	325
Premises	98	70	251	217
Depreciation of fixed assets	56	42	138	124
Amortization and impairment of intangible assets	36	50	112	205
Other general expense	1,348	288	1,955	892
Total operating expenses	3,503	1,944	7,997	6,033
Operating income (loss)	(801)	441	1,116	2,068
Interest income	3	3	9	5
Interest expense	(80)	(80)	(237)	(252)
Other income (expense)	10	0	7	19
Income (loss) before income taxes	(868)	364	895	1,840
Income tax expense	23	82	460	356
Net income (loss)	(891)	282	435	1,484
Less: Net income attributable to noncontrolling interests	9	7	43	39
Net income (loss) attributable to Aon shareholders	$ (900)	$ 275	$ 392	$ 1,445
Basic net income (loss) per share attributable to Aon shareholders (in dollars per share)	$ (3.99)	$ 1.18	$ 1.73	$ 6.21
Diluted net income (loss) per share attributable to Aon shareholders (in dollars per share)	$ (3.99)	$ 1.18	$ 1.72	$ 6.18
Weighted average ordinary shares outstanding - basic (in shares)	225.4	232.6	226.5	232.8
Weighted average ordinary shares outstanding - diluted (in shares)	225.4	233.5	227.7	233.9