Debt Schedule of Debt Instruments (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 2,221.8	$ 2,221.8
Less unamortized discount	(3.5)	(3.7)
Long-term Debt	2,218.3	2,218.1
Revolving Credit Facility due 2019 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	0	0
Senior Notes Due 2016 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	176.8	176.8
Senior Notes Due 2018 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	134.0	134.0
Senior Notes Due 2020 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	136.0	136.0
Senior Notes Due 2021 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	625.0	625.0
Senior Notes Due 2022 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	500.0	500.0
5.25% Senior Notes Due 2023 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 650.0	$ 650.0