Fair Value Measurements (Carrying Values And Fair Values Of Assets and Liabilities Not Required to be Carried at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Apr. 01, 2021	Mar. 31, 2021
Other Non-Current Assets | Interest rate swaps, financing element
Fair Value, Carrying Values and Fair Values of Assets and Liabilities Not Required to be Carried at Fair Value on a Recurring Basis [Line Items]
Financing element of certain hybrid instruments	$ 93.1		$ 98.2
Senior Notes | 5.500% Senior Notes
Fair Value, Carrying Values and Fair Values of Assets and Liabilities Not Required to be Carried at Fair Value on a Recurring Basis [Line Items]
Coupon rate	5.50%	5.50%
Senior Notes | 5.875% Senior Notes
Fair Value, Carrying Values and Fair Values of Assets and Liabilities Not Required to be Carried at Fair Value on a Recurring Basis [Line Items]
Coupon rate	5.875%	5.875%
Senior Notes | 6.375% Senior Notes
Fair Value, Carrying Values and Fair Values of Assets and Liabilities Not Required to be Carried at Fair Value on a Recurring Basis [Line Items]
Coupon rate	6.375%	6.375%
Carrying Value
Fair Value, Carrying Values and Fair Values of Assets and Liabilities Not Required to be Carried at Fair Value on a Recurring Basis [Line Items]
Financing component of interest rate swaps, fair value disclosure	$ 143.3		152.5
Carrying Value | Term Loan | Term Loan A
Fair Value, Carrying Values and Fair Values of Assets and Liabilities Not Required to be Carried at Fair Value on a Recurring Basis [Line Items]
Loans, fair value disclosure	641.3		651.4
Carrying Value | Term Loan | Term Loan B
Fair Value, Carrying Values and Fair Values of Assets and Liabilities Not Required to be Carried at Fair Value on a Recurring Basis [Line Items]
Loans, fair value disclosure	842.7		942.8
Carrying Value | Senior Notes | 5.500% Senior Notes
Fair Value, Carrying Values and Fair Values of Assets and Liabilities Not Required to be Carried at Fair Value on a Recurring Basis [Line Items]
Senior Notes, fair value disclosure	963.8		0.0
Carrying Value | Senior Notes | 5.875% Senior Notes
Fair Value, Carrying Values and Fair Values of Assets and Liabilities Not Required to be Carried at Fair Value on a Recurring Basis [Line Items]
Senior Notes, fair value disclosure	0.0		506.7
Carrying Value | Senior Notes | 6.375% Senior Notes
Fair Value, Carrying Values and Fair Values of Assets and Liabilities Not Required to be Carried at Fair Value on a Recurring Basis [Line Items]
Senior Notes, fair value disclosure	0.0		540.8
Carrying Value | Production And Related Loans | Production And Related Loans
Fair Value, Carrying Values and Fair Values of Assets and Liabilities Not Required to be Carried at Fair Value on a Recurring Basis [Line Items]
Loans, fair value disclosure	867.5		489.0
Carrying Value | Line of Credit | IP Credit Facility And Other Financing Obligations
Fair Value, Carrying Values and Fair Values of Assets and Liabilities Not Required to be Carried at Fair Value on a Recurring Basis [Line Items]
IP Credit Facility and other financing obligations, fair value disclosure	212.3		0.0
Fair Value | Fair Value (Level 2)
Fair Value, Carrying Values and Fair Values of Assets and Liabilities Not Required to be Carried at Fair Value on a Recurring Basis [Line Items]
Financing component of interest rate swaps, fair value disclosure	136.6		144.7
Fair Value | Fair Value (Level 2) | Term Loan | Term Loan A
Fair Value, Carrying Values and Fair Values of Assets and Liabilities Not Required to be Carried at Fair Value on a Recurring Basis [Line Items]
Loans, fair value disclosure	620.8		647.6
Fair Value | Fair Value (Level 2) | Term Loan | Term Loan B
Fair Value, Carrying Values and Fair Values of Assets and Liabilities Not Required to be Carried at Fair Value on a Recurring Basis [Line Items]
Loans, fair value disclosure	844.0		936.0
Fair Value | Fair Value (Level 2) | Senior Notes | 5.500% Senior Notes
Fair Value, Carrying Values and Fair Values of Assets and Liabilities Not Required to be Carried at Fair Value on a Recurring Basis [Line Items]
Senior Notes, fair value disclosure	1,027.5		0.0
Fair Value | Fair Value (Level 2) | Senior Notes | 5.875% Senior Notes
Fair Value, Carrying Values and Fair Values of Assets and Liabilities Not Required to be Carried at Fair Value on a Recurring Basis [Line Items]
Senior Notes, fair value disclosure	0.0		533.9
Fair Value | Fair Value (Level 2) | Senior Notes | 6.375% Senior Notes
Fair Value, Carrying Values and Fair Values of Assets and Liabilities Not Required to be Carried at Fair Value on a Recurring Basis [Line Items]
Senior Notes, fair value disclosure	0.0		563.0
Fair Value | Fair Value (Level 2) | Production And Related Loans | Production And Related Loans
Fair Value, Carrying Values and Fair Values of Assets and Liabilities Not Required to be Carried at Fair Value on a Recurring Basis [Line Items]
Loans, fair value disclosure	871.9		493.5
Fair Value | Fair Value (Level 2) | Line of Credit | IP Credit Facility And Other Financing Obligations
Fair Value, Carrying Values and Fair Values of Assets and Liabilities Not Required to be Carried at Fair Value on a Recurring Basis [Line Items]
IP Credit Facility and other financing obligations, fair value disclosure	$ 215.0		$ 0.0