Fair Value Measurements (Narrative) (Details) Share data in Millions, except Per Share data, unless otherwise specified	12 Months Ended				12 Months Ended
	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Mar. 31, 2011 interest_rate_swap	Dec. 31, 2014 Senior Debt Obligations Due 2014 [Member] USD ($)	Dec. 31, 2014 Interest Rate Swap [Member]	Dec. 31, 2014 Minimum [Member]	Dec. 31, 2013 Minimum [Member]	Dec. 31, 2014 Maximum [Member]	Dec. 31, 2013 Maximum [Member]	Dec. 31, 2014 Private Equity Funds [Member] USD ($)	Dec. 31, 2013 Private Equity Funds [Member] USD ($)	Dec. 31, 2014 Alexander Forbes Group Holdings Limited [Member] USD ($)	Dec. 31, 2014 Alexander Forbes Group Holdings Limited [Member] ZAR	Jun. 30, 2014 Mercer Consulting Group [Member] Alexander Forbes Group Holdings Limited [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value interest rate swap discount rate					1.60%
Number of interest rate swaps to convert fixed interest rate on notes to floating rate			2
Fair value measurement on senior notes subject to interest rate swaps				$ 250,000,000
Revenue target period (in years)						2 years	2 years	4 years	4 years
Assets transferred between Level 1 and Level 2	0
Adjustments to acquisition related contingent consideration liability	31,000,000
Increase in fair value of contingent consideration due to 5% increase in projections	22,000,000
Decrease in fair value of contingent consideration due to 5% decrease in projections	26,000,000
Carrying value of equity method investments	388,000,000	89,000,000								61,000,000	38,000,000	282,000,000
Percentage of interest acquired														34.00%
Equity investment shares owned by the Company												443	443
Share price													9.5
Market value of equity method investment													362,000,000