Consolidated Statements of Income (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Revenue
Commissions, fees and other	$ 3,292	$ 2,873	$ 2,913	$ 2,941	$ 3,202	$ 2,786	$ 2,891	$ 2,908	$ 12,019		$ 11,787		$ 11,476
Fiduciary investment income	7	7	6	6	7	8	6	7	26		28		38
Total revenue	3,299	2,880	2,919	2,947	3,209	2,794	2,897	2,915	12,045		11,815		11,514
Expenses
Compensation and benefits									7,014		6,945		6,709
Other general expenses									3,065		3,199		3,209
Total operating expenses									10,079		10,144		9,918
Operating income	635	417	445	469	515	364	382	410	1,966		1,671		1,596
Interest income									10		9		10
Interest expense									(255)		(210)		(228)
Other income									44		68		2
Income before income taxes									1,765		1,538		1,380
Income taxes									334		390		360
Net income	467	315	313	336	360	264	252	272	1,431		1,148		1,020
Less: Net income attributable to noncontrolling interests	8	6	9	11	5	8	11	11	34		35		27
Net income attributable to Aon shareholders	$ 459	$ 309	$ 304	$ 325	$ 355	$ 256	$ 241	$ 261	$ 1,397		$ 1,113		$ 993
Basic net income per share attributable to Aon shareholders (in dollars per share)	$ 1.60	$ 1.06	$ 1.02	$ 1.07					$ 4.73		$ 3.57		$ 3.02
Diluted net income per share attributable to Aon shareholders (in dollars per share)	$ 1.56	$ 1.04	$ 1.01	$ 1.06					$ 4.66		$ 3.53		$ 2.99
Cash dividends per share paid on ordinary shares (in dollars per share)	$ 0.25	$ 0.25	$ 0.25	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.16	$ 0.92		$ 0.68		$ 0.62
Weighted average ordinary shares outstanding - basic (in shares)									295.5	[1]	311.4	[1]	328.5	[1]
Weighted average ordinary shares outstanding - diluted (in shares)									299.6		315.4		332.6

[1] Includes 3.0 million, 3.9 million and 4.7 million shares of participating securities for the years ended December 31, 2014, 2013, and 2012 respectively.