Consolidated Statements of Shareholders' Equity (USD $) In Millions, unless otherwise specified	Total	Ordinary Shares and Additional Paid-in Capital	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Loss, Net of Tax	Noncontrolling Interests
Balance at Dec. 31, 2009	$ 5,431	$ 3,578	$ 7,379	$ (3,859)	$ (1,719)	$ 52
Balance (in shares) at Dec. 31, 2009		362.7
Increase (Decrease) in Shareholders' Equity
Net income	732		706			26
Retirement of treasury shares		(1,660)		1,660
Retirement of treasury shares (in shares)		(40.0)
Shares issued - Hewitt acquisition	2,474	2,474
Shares issued - Hewitt acquisition (in shares)		61.0
Shares issued - employee benefit plans	135	135
Shares issued - employee benefit plans (in shares)		2.2
Shares purchased	(250)			(250)
Shares reissued - employee benefit plans	(49)	(370)	(49)	370
Tax benefit - employee benefit plans	20	20
Share-based compensation expense	221	221
Dividends to shareholders	(175)		(175)
Change in net derivative gains/losses	(24)				(24)
Net foreign currency translation adjustments	(135)				(133)	(2)
Net post-retirement benefit obligation	(41)				(41)
Purchase of subsidiary shares from non-controlling interests	(15)	(12)				(3)
Capital contribution by noncontrolling interests	2					2
Dividends paid to non-controlling interests on subsidiary common stock	(20)					(20)
Balance at Dec. 31, 2010	8,306	4,386	7,861	(2,079)	(1,917)	55
Balance (in shares) at Dec. 31, 2010		385.9
Increase (Decrease) in Shareholders' Equity
Net income	1,010		979			31
Shares issued - employee benefit plans	112	113	(1)
Shares issued - employee benefit plans (in shares)		0.5
Shares purchased	(828)			(828)
Shares reissued - employee benefit plans	(45)	(354)	(45)	354
Tax benefit - employee benefit plans	36	36
Share-based compensation expense	235	235
Dividends to shareholders	(200)		(200)
Change in net derivative gains/losses	(13)				(13)
Net foreign currency translation adjustments	(43)				(44)	1
Net post-retirement benefit obligation	(396)				(396)
Purchase of subsidiary shares from non-controlling interests	(24)	(9)				(15)
Dividends paid to non-controlling interests on subsidiary common stock	(30)					(30)
Balance at Dec. 31, 2011	8,120	4,407	8,594	(2,553)	(2,370)	42
Balance (in shares) at Dec. 31, 2011	386.4	386.4
Increase (Decrease) in Shareholders' Equity
Net income	1,020		993			27
Retirement of treasury shares		(60)	(2,412)	2,472
Retirement of treasury shares (in shares)		(60.0)
Shares issued - employee benefit plans	29	29
Shares issued - employee benefit plans (in shares)		4.0
Shares purchased	(1,125)		(1,025)	(100)
Shares purchased (in shares)		(19.5)
Shares reissued - employee benefit plans	(13)	(181)	(13)	181
Tax benefit - employee benefit plans	33	33
Share-based compensation expense	212	212
Dividends to shareholders	(204)		(204)
Change in net derivative gains/losses	9				9
Net foreign currency translation adjustments	109				109
Net post-retirement benefit obligation	(358)				(358)
Purchase of subsidiary shares from non-controlling interests		(1)				1
Dividends paid to non-controlling interests on subsidiary common stock	(27)					(27)
Balance at Dec. 31, 2012	$ 7,805	$ 4,439	$ 5,933		$ (2,610)	$ 43
Balance (in shares) at Dec. 31, 2012	310.9	310.9