Investments - Equity Method LLCs (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Investments Disclosures [Abstract]
Equity Method Investment, Summarized Financial Information, Assets	$ 3,643.6	$ 4,086.9
Equity Method Investment, Summarized Financial Information, Liabilities	421.0	440.2
Equity Method Investment, Summarized Financial Information, Net Income (Loss)	134.6	(13.8)	401.6
Equity Method Limited Liability Investments at Cost Plus Cumulative Undistributed Earnings	253.0	306.3
Outstanding Commitments to Fund Equity Method Limited Liability Investments	$ 52.8