Income Taxes - Valuation Allowance (Details 3) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of year	$ 764.1	$ 873.1	$ 22.3
Balance at end of year	1,000.4	764.1	873.1
Valuation Allowance, Deferred Tax Asset, Change in Beginning of the Year Amount	(1.2)	(1.6)	735.2
Included in income tax expense (benefit) [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Change in valuation allowance	36.7	21.9	865.5
Change in deferred assets related to other comprehensive income [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Change in valuation allowance	199.6	(130.9)	0
Included in stockholders' equity related to issuance of exchangeable debt [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Change in valuation allowance	$ 0	$ 0	$ (14.7)