Debt (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 1,864.3	$ 1,864.3	$ 2,015.6
Letters of credit outstanding			2.9
Principal amount of senior notes outstanding	1,877.2	$ 1,877.2
Senior Notes, stated interest rate, minimum (in hundredths)		5.25%
Senior Notes, stated interest rate, maximim (in hundredths)		6.875%
Senior Note Repurchase Capacity	500.0	$ 500.0
Subsidiary Guarantee Issuance Capacity	500.0	500.0
Gain (Loss) on Extinguishment of Debt, before Write off of Debt Issuance Cost		27.5
Write off of Deferred Debt Issuance Cost	1.5
Revolving Credit Facility due 2022 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	0.0	0.0	0.0
Borrowing capacity	850.0	850.0
Letters of credit outstanding	10.9	10.9
6.875% Senior Notes Due 2021 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 275.3	$ 275.3	382.4
Long-term debt, interest rate (in hundredths)	6.875%	6.875%
Extinguishment of Debt, Amount		$ 107.1
5.375% Senior Notes Due 2022 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 465.1	$ 465.1	500.0
Long-term debt, interest rate (in hundredths)	5.375%	5.375%
Extinguishment of Debt, Amount		$ 34.9
Senior Notes Due 2023 [Member]
Debt Instrument [Line Items]
Long-term debt, interest rate (in hundredths)	5.25%	5.25%
Extinguishment of Debt, Amount		$ 13.2
Senior Notes Due 2026 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 500.0	$ 500.0	$ 500.0