Condensed Consolidated Statements of Income (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Revenue
Commissions, fees and other	$ 2,891	$ 2,813	$ 5,799	$ 5,642
Fiduciary investment income	6	8	13	20
Total revenue	2,897	2,821	5,812	5,662
Expenses
Compensation and benefits	1,712	1,639	3,437	3,300
Other general expenses	803	788	1,583	1,566
Total operating expenses	2,515	2,427	5,020	4,866
Operating income	382	394	792	796
Interest income	2	2	3	5
Interest expense	(48)	(57)	(100)	(116)
Other income	6	12	15	12
Income from continuing operations before income taxes	342	351	710	697
Income taxes	90	96	186	193
Income from continuing operations	252	255	524	504
Loss from discontinued operations before income taxes	0	(1)	0	(1)
Income taxes	0	0	0	0
Loss from discontinued operations	0	(1)	0	(1)
Net income	252	254	524	503
Less: Net income attributable to noncontrolling interests	11	8	22	19
Net income attributable to Aon shareholders	241	246	502	484
Net income (loss) attributable to Aon shareholders
Income from continuing operations	241	247	502	485
Loss from discontinued operations	0	(1)	0	(1)
Net income attributable to Aon shareholders	$ 241	$ 246	$ 502	$ 484
Basic net income per share attributable to Aon shareholders
Continuing operations (in dollars per share)	$ 0.77	$ 0.74	$ 1.59	$ 1.46
Discontinued operations (in dollars per share)	$ 0.00	$ 0.00	$ 0.00	$ 0.00
Net income (in dollars per share)	$ 0.77	$ 0.74	$ 1.59	$ 1.46
Diluted net income per share attributable to Aon shareholders
Continuing operations (in dollars per share)	$ 0.76	$ 0.73	$ 1.58	$ 1.44
Discontinued operations (in dollars per share)	$ 0.00	$ 0.00	$ 0.00	$ 0.00
Net income (in dollars per share)	$ 0.76	$ 0.73	$ 1.58	$ 1.44
Cash dividends per share paid on ordinary shares (in dollars per share)	$ 0.18	$ 0.16	$ 0.33	$ 0.31
Weighted average ordinary shares outstanding - basic	313.7	332.0	315.0	332.2
Weighted average ordinary shares outstanding - diluted	317.1	335.6	318.6	336.1