Condensed Consolidated Statements of Income (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenue
Total revenue	$ 2,349	$ 2,340	$ 8,000	$ 7,089
Expenses
Compensation and benefits	1,392	1,428	4,502	4,363
Information technology	125	109	363	295
Premises	94	89	283	259
Depreciation of fixed assets	40	40	126	148
Amortization and impairment of intangible assets	100	101	492	604
Other general expenses	336	317	1,189	956
Total operating expenses	2,087	2,084	6,955	6,625
Operating income	262	256	1,045	464
Interest income	0	10	5	20
Interest expense	(69)	(70)	(208)	(211)
Other income (expense)	1	4	(17)	6
Income from continuing operations before income taxes	194	200	825	279
Income tax expense (benefit)	39	4	9	(139)
Net income from continuing operations	155	196	816	418
Net income (loss) from discontinued operations	(2)	(4)	5	857
Net income	153	192	821	1,275
Less: Net income attributable to noncontrolling interests	6	7	32	30
Net income attributable to Aon shareholders	$ 147	$ 185	$ 789	$ 1,245
Basic net income (loss) per share attributable to Aon shareholders
Basic net income (loss) per share attributable to Aon shareholders, continuing operations (in dollars per share)	$ 0.61	$ 0.74	$ 3.18	$ 1.49
Basic net income (loss) per share attributable to Aon shareholders, discontinued operations (in dollars per share)	(0.01)	(0.02)	0.02	3.28
Basic net income (loss) per share attributable to Aon shareholders (in dollars per share)	0.60	0.72	3.20	4.77
Diluted net income (loss) per share attributable to Aon shareholders
Diluted net income (loss) per share attributable to Aon shareholders, continuing operations (in dollars per share)	0.61	0.73	3.17	1.48
Diluted net income (loss) per share attributable to Aon shareholders, discontinued operations (in dollars per share)	(0.01)	(0.01)	0.02	3.26
Diluted net income (loss) per share attributable to Aon shareholders (in dollars per share)	0.60	0.72	3.19	4.74
Cash dividends per share paid on ordinary shares (in dollars per share)	$ 0.4	$ 0.36	$ 1.16	$ 1.05
Weighted average ordinary shares outstanding - basic (in shares)	244.0	255.6	246.2	260.9
Weighted average ordinary shares outstanding - diluted (in shares)	245.6	257.3	247.7	262.9