Fair Value Measurements (Narrative) (Details) (USD $)	3 Months Ended	9 Months Ended				9 Months Ended				9 Months Ended
	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2012	Mar. 31, 2012 interest_rate_swap	Feb. 28, 2011 interest_rate_swap	Sep. 30, 2013 Minimum [Member]	Sep. 30, 2013 Maximum [Member]	Sep. 30, 2013 Senior Debt Obligations Due 2014 [Member]	Feb. 28, 2011 Senior Debt Obligations Due 2014 [Member]	Sep. 30, 2013 Interest Rate Swap [Member]	Sep. 30, 2013 Private Equity Funds [Member]	Dec. 31, 2012 Private Equity Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value interest rate swap discount rate										1.60%
Fair value interest rate swap derivatives								$ 250,000,000	$ 250,000,000
Number of interest rate swaps to convert fixed interest rate on notes to floating rate				2	2
Revenue target period (in years)						2 years	4 years
Adjustments to acquisition related contingent consideration liability		16,000,000	(32,000,000)
Increase in fair value of contingent consideration due to 5% increase in projections	15,000,000
Decrease in fair value of contingent consideration due to 5% decrease in projections	13,000,000
Long-term investments, cost basis											$ 12,000,000	$ 16,000,000