Long-Term Debt Senior Notes (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended			3 Months Ended		9 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014	Mar. 31, 2014	Sep. 30, 2014	Dec. 01, 2014	Aug. 05, 2014	Mar. 20, 2014
Debt Instrument [Line Items]
Payments for Derivative Instrument, Investing Activities	$ 2.1	$ 0	$ 0.3
Proceeds from issuance of long-term debt	1,175.0	1,535.2	135.7
Debt, long-term and short-term	3,192.4			3,192.4
Deferred financing costs, net	33.0	30.1	53.2	33.0
Gains (Losses) on Extinguishment of Debt	(90.7)	(64.0)	(17.2)
Write off of Deferred Debt Issuance Cost	12.6	20.1
Senior notes due 2019 [Member]
Debt Instrument [Line Items]
Long-term debt, stated interest rate	8.50%			8.50%
Redemption Premium, percentage of par value							106.202%	108.764%	109.75%
Extinguishment of Debt, Accrued Interest Paid to Lenders									1.0
Debt, long-term and short-term	503.9	1,305.0		503.9
Premium, Unamortized	1.3	4.2		1.3
Debt Instrument, Repurchased Face Amount							541.4	234.7	25.0
Gains (Losses) on Extinguishment of Debt	36.9			22.1		2.7
Write off of Deferred Debt Issuance Cost	4.7			2.2	0.3
Extinguishment of Debt, Fees Paid to Lenders	23.0			10.0	2.4
Extinguishment of Debt, Make-whole Interest Payment	10.6			10.6
Write off of Deferred Debt issuance Cost, unamortized premium	1.4			0.7
Senior Notes due 2022 [Member]
Debt Instrument [Line Items]
Long-term debt, stated interest rate	6.00%			6.00%
Debt, long-term and short-term	600.0			600.0
Premium, Unamortized		0
Deferred financing costs, net	8.0			8.0
Senior Notes due 2024 [Member]
Debt Instrument [Line Items]
Long-term debt, stated interest rate	5.50%			5.50%
Debt, long-term and short-term	575.0			575.0
Premium, Unamortized		0
Deferred financing costs, net	7.5			7.5
Cap agreement effective January 14, 2015-2017 [Member]
Debt Instrument [Line Items]
Payments for Derivative Instrument, Investing Activities	2.1
Derivative Asset, Noncurrent	1.7			1.7
Derivative, Notional Amount	$ 1,000.0			$ 1,000.0