Debt and Other Financing Debt and Other Financing (Schedule of Public Notes) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Five Point Seven Five Percent Notes, Due March Two Thousand Eighteen [Member]
Debt Instrument [Line Items]
Remaining Principal	$ 0.0	$ 250.0
Unamortized Discounts	0.0	(0.2)
Unamortized Debt Issuance Costs	0.0	(0.4)
Total	0.0	249.4
Four Point Two Percent Notes, Due July Two Thousand Eighteen [Member]
Debt Instrument [Line Items]
Remaining Principal	0.0	250.0
Unamortized Discounts	0.0	(0.2)
Unamortized Debt Issuance Costs	0.0	(0.2)
Total	0.0	249.6
Six Point Five Percent Notes, Due March Two Thousand Nineteen [Member]
Debt Instrument [Line Items]
Remaining Principal	237.9	350.0
Unamortized Discounts	(0.7)	(1.4)
Unamortized Debt Issuance Costs	(0.4)	(0.9)
Total	236.8	347.7
Four Point Six Zero Percent Notes, Due March Two Thousand Twenty [Member]
Debt Instrument [Line Items]
Remaining Principal	409.9	500.0
Unamortized Discounts	(0.3)	(0.4)
Unamortized Debt Issuance Costs	(1.4)	(2.3)
Total	408.2	497.3
Five Point Zero Percent Notes, Due March Two Thousand Twenty-Three [Member]
Debt Instrument [Line Items]
Remaining Principal	488.9	500.0
Unamortized Discounts	(2.9)	(3.5)
Unamortized Debt Issuance Costs	(2.3)	(2.8)
Total	483.7	493.7
Six Point Nine Five Percent Notes, Due March Two Thousand Forty-Three [Member]
Debt Instrument [Line Items]
Remaining Principal	243.8	250.0
Unamortized Discounts	(0.6)	(0.7)
Unamortized Debt Issuance Costs	(2.4)	(2.5)
Total	$ 240.8	$ 246.8