Condensed Consolidated Statements of Income (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Revenue
Commissions, fees and other	$ 2,726	$ 2,708	$ 8,368	$ 8,255
Fiduciary investment income	11	15	31	38
Total revenue	2,737	2,723	8,399	8,293
Expenses
Compensation and benefits	1,620	1,634	4,920	4,843
Other general expenses	778	761	2,344	2,284
Total operating expenses	2,398	2,395	7,264	7,127
Operating income	339	328	1,135	1,166
Interest income	1	4	6	14
Interest expense	(57)	(60)	(173)	(186)
Other (expense) income	(9)	20	3	6
Income from continuing operations before income taxes	274	292	971	1,000
Income taxes	64	84	257	274
Income from continuing operations	210	208	714	726
(Loss) income from discontinued operations before income taxes			(1)	5
Income taxes				1
(Loss) income from discontinued operations			(1)	4
Net income	210	208	713	730
Less: Net income attributable to noncontrolling interests	6	10	25	28
Net income attributable to Aon shareholders	204	198	688	702
Net income (loss) attributable to Aon shareholders
Income from continuing operations	204	198	689	698
(Loss) income from discontinued operations			(1)	4
Net income	$ 204	$ 198	$ 688	$ 702
Basic net income per share attributable to Aon shareholders
Continuing operations (in dollars per share)	$ 0.62	$ 0.59	$ 2.08	$ 2.07
Discontinued operations (in dollars per share)				$ 0.01
Net income (in dollars per share)	$ 0.62	$ 0.59	$ 2.08	$ 2.08
Diluted net income per share attributable to Aon shareholders
Continuing operations (in dollars per share)	$ 0.62	$ 0.59	$ 2.06	$ 2.04
Discontinued operations (in dollars per share)				$ 0.01
Net income (in dollars per share)	$ 0.62	$ 0.59	$ 2.06	$ 2.05
Cash dividends per share paid on ordinary shares (in dollars per share)	$ 0.16	$ 0.15	$ 0.46	$ 0.45
Weighted average ordinary shares outstanding - basic (in shares)	327.3	332.6	330.6	336.7
Weighted average ordinary shares outstanding - diluted (in shares)	331.0	336.9	334.4	341.8