Condensed Consolidated Statements of Income (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Revenue
Commissions, fees and other	$ 2,813	$ 2,799	$ 5,642	$ 5,547
Fiduciary investment income	8	12	20	23
Total revenue	2,821	2,811	5,662	5,570
Expenses
Compensation and benefits	1,639	1,612	3,300	3,209
Other general expenses	788	759	1,566	1,523
Total operating expenses	2,427	2,371	4,866	4,732
Operating income	394	440	796	838
Interest income	2	4	5	10
Interest expense	(57)	(63)	(116)	(126)
Other income (expense)	12	(29)	12	(14)
Income from continuing operations before income taxes	351	352	697	708
Income taxes	96	87	193	190
Income from continuing operations	255	265	504	518
(Loss) income from discontinued operations before income taxes	(1)	1	(1)	5
Income tax (benefit) expense		(1)		1
(Loss) income from discontinued operations	(1)	2	(1)	4
Net income	254	267	503	522
Less: Net income attributable to noncontrolling interests	8	9	19	18
Net income attributable to Aon shareholders	246	258	484	504
Net income (loss) attributable to Aon shareholders
Income from continuing operations	247	256	485	500
(Loss) income from discontinued operations	(1)	2	(1)	4
Net income	$ 246	$ 258	$ 484	$ 504
Basic net income per share attributable to Aon shareholders
Continuing operations (in dollars per share)	$ 0.74	$ 0.76	$ 1.46	$ 1.48
Discontinued operations (in dollars per share)				$ 0.01
Net income (in dollars per share)	$ 0.74	$ 0.76	$ 1.46	$ 1.49
Diluted net income per share attributable to Aon shareholders
Continuing operations (in dollars per share)	$ 0.73	$ 0.75	$ 1.44	$ 1.45
Discontinued operations (in dollars per share)				$ 0.01
Net income (in dollars per share)	$ 0.73	$ 0.75	$ 1.44	$ 1.46
Cash dividends per share paid on ordinary shares (in dollars per share)	$ 0.16	$ 0.15	$ 0.31	$ 0.3
Weighted average ordinary shares outstanding - basic (in shares)	332.0	337.7	332.2	338.7
Weighted average ordinary shares outstanding - diluted (in shares)	335.6	342.7	336.1	344.0