Condensed Consolidated Statements of Income (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Revenue
Commissions, fees and other	$ 2,829	$ 2,748
Fiduciary investment income	12	11
Total revenue	2,841	2,759
Expenses
Compensation and benefits	1,661	1,597
Other general expenses	778	764
Total operating expenses	2,439	2,361
Operating income	402	398
Interest income	3	6
Interest expense	(59)	(63)
Other income		15
Income from continuing operations before income taxes	346	356
Income taxes	97	103
Income from continuing operations	249	253
Income from discontinued operations before income taxes		4
Income taxes		2
Income from discontinued operations		2
Net income	249	255
Less: Net income attributable to noncontrolling interests	11	9
Net income attributable to Aon stockholders	238	246
Net income attributable to Aon stockholders
Income from continuing operations	238	244
Income from discontinued operations		2
Net income	$ 238	$ 246
Basic net income per share attributable to Aon stockholders
Continuing operations (in dollars per share)	$ 0.72	$ 0.72
Discontinued operations (in dollars per share)	$ 0.00
Net income (in dollars per share)	$ 0.72	$ 0.72
Diluted net income per share attributable to Aon stockholders
Continuing operations (in dollars per share)	$ 0.71	$ 0.71
Discontinued operations (in dollars per share)	$ 0.00
Net income (in dollars per share)	$ 0.71	$ 0.71
Cash dividends per share paid on common stock (in dollars per share)	$ 0.15	$ 0.15
Weighted average common shares outstanding - basic (in shares)	332.4	339.4
Weighted average common shares outstanding - diluted (in shares)	336.6	345.4