Long-Term Debt Senior Subordinated Notes (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended			0 Months Ended	1 Months Ended	3 Months Ended			1 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Mar. 08, 2013	Feb. 28, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jul. 31, 2013	Apr. 30, 2013	Jul. 02, 2013	May 09, 2014	Feb. 21, 2014	Jan. 22, 2014	Oct. 18, 2013	Aug. 01, 2013	Mar. 10, 2010	Sep. 30, 2014
Debt Instrument [Line Items]
Debt, long-term and short-term	$ 3,192.4
Proceeds from issuance of long-term debt	1,175.0	1,535.2	135.7
Proceeds from exercise in full of overallotment option											56.0
Gains (Losses) on Extinguishment of Debt	90.7	64.0	17.2
Write off of Deferred Debt Issuance Cost	12.6	20.1
Subordinated Debt [Member]
Debt Instrument [Line Items]
Long-term debt, stated interest rate	12.535%
Debt, long-term and short-term	0	92.5					92.5
Debt Instrument, Repurchased Face Amount				50.0		50.0						42.5	20.0	30.0	155.0	324.0	28.5
Redemption Premium, percentage of par value				106.268%								104.178%	104.178%		104.178%	106.268%
Gains (Losses) on Extinguishment of Debt	(2.2)			3.9		2.7	8.5	24.6
Extinguishment of Debt, Fees Paid to Lenders	1.8			3.1		2.1	6.5	20.3
Write off of Deferred Debt Issuance Cost	0.4			0.8	0.6		2.0	4.3
Extinguishment of Debt, Accrued Interest Paid to Lenders				2.5								0.4	1.9		0.2	12.0
Senior Subordinated Notes [Member]
Debt Instrument [Line Items]
Debt, long-term and short-term																		0
Term Loan [Member]
Debt Instrument [Line Items]
Debt, long-term and short-term	1,513.5	1,528.9					1,528.9
Debt Instrument, Face Amount									190.0
Proceeds from issuance of long-term debt										1,350.0
Gains (Losses) on Extinguishment of Debt		10.3
IPO Proceeds [Member] | Subordinated Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Repurchased Face Amount																146.0
Term Loan Incremental Borrowings [Member] | Subordinated Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Repurchased Face Amount																$ 178.0