Investments - Equity Method LLCs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Investments, Debt and Equity Securities [Abstract]
Equity Method Investment, Summarized Financial Information, Assets	$ 3,801.7	$ 3,349.7
Equity Method Investment, Summarized Financial Information, Liabilities	879.1	711.5
Equity Method Investment, Summarized Financial Information, Net Income (Loss)	159.6	96.2	$ 181.1
Equity method limited liability investments at cost plus cumulative undistributed earnings	190.6	$ 184.8
Outstanding commitments to fund equity method limited liability investments	$ 58.8