Share-Based Compensation Plans (Details 2) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended				12 Months Ended
	Dec. 31, 2011 All Other Option Plans	Dec. 31, 2010 All Other Option Plans	Dec. 31, 2012 Hewitt Associates, Inc (Hewitt)	Oct. 02, 2010 Hewitt Associates, Inc (Hewitt)	Dec. 31, 2012 Share options	Dec. 31, 2011 Share options	Dec. 31, 2010 Share options	Dec. 31, 2012 Share options Leadership Performance Plan ("LPP") cycle	Dec. 31, 2011 Share options Incentive compensation plans	Dec. 31, 2010 Share options Incentive compensation plans
Employee Share Options and Share Awards
Continuous years of service before options begin to vest					2 years
Vesting period					4 years			3 years
Continuous years of service before all options would vest for those options that do not vest incrementally					5 years
Maximum contractual term					10 years			6 years
Weighted Average assumptions, weighted average expected life and estimated fair value of options
Weighted average volatility (as a percent)	26.10%	28.50%
Expected dividend yield (as a percent)	1.30%	1.60%
Risk-free rate (as a percent)	2.20%	3.00%
Weighted average expected life	5 years 6 months	6 years 1 month 6 days
Weighted average estimated fair value per share	$ 10.92	$ 10.37
Share Options
Outstanding at beginning of period (in shares)			600	600	9,116	13,919	15,937
Options issued in connection with the Hewitt acquisition (in shares)							4,545
Granted (in shares)						80	143		80	143
Exercised (in shares)					(3,413)	(4,546)	(6,197)
Forfeited and expired (in shares)					(92)	(337)	(509)
Outstanding at end of period (in shares)			600	600	5,611	9,116	13,919
Exercisable at end of period (in shares)			600	600	5,117	7,833	11,293
Shares available for grant (in shares)				4,500	17,024	24,508	22,777
Weighted-Average Exercise Price
Outstanding at beginning of period (in dollars per share)					$ 32	$ 32	$ 33
Options issued in connection with the Hewitt acquisition (in dollars per share)							$ 22
Granted (in dollars per share)						$ 53	$ 38		$ 53	$ 38
Exercised (in dollars per share)					$ 31	$ 32	$ 27
Forfeited and expired (in dollars per share)					$ 37	$ 36	$ 35
Outstanding at end of period (in dollars per share)					$ 32	$ 32	$ 32
Exercisable at end of period (in dollars per share)					$ 31	$ 30	$ 30