Chapter 11 Proceedings and Ability to Continue as Going Concern - Schedule of Liabilities Subject to Compromise (Details) - USD ($) $ in Millions	Dec. 31, 2020	Aug. 18, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Liabilities Subject To Compromise, Accrued Interest On Notes	$ 203.5
Liabilities Subject To Compromise, Holding Cost, Inclusive Of Interest	13.9
Liabilities Subject to Compromise, Total	7,313.7		$ 0.0
Senior Notes [Member] \| 6.875% Senior notes due 2020
Debt Instrument [Line Items]
Liabilities Subject To Compromise, Long-term Debt	122.9
Debtor-in-Possession Financing, Interest Rate on Borrowings Outstanding		6.875%
Senior Notes [Member] \| Four Point Seven Zero Percent Senior Notes Due Twenty Twenty One [Member]
Debt Instrument [Line Items]
Liabilities Subject To Compromise, Long-term Debt	100.7
Debtor-in-Possession Financing, Interest Rate on Borrowings Outstanding		4.70%
Senior Notes [Member] \| Four Point Eight Seven Five Percent Senior Notes Due Twenty Twenty Two [Member]
Debt Instrument [Line Items]
Liabilities Subject To Compromise, Long-term Debt	620.8
Debtor-in-Possession Financing, Interest Rate on Borrowings Outstanding		4.875%
Senior Notes [Member] \| Three Point Zero Percent Exchangeable Senior Notes Due Twenty Twenty Four [Member]
Debt Instrument [Line Items]
Liabilities Subject To Compromise, Long-term Debt	849.5
Debtor-in-Possession Financing, Interest Rate on Borrowings Outstanding		3.00%
Senior Notes [Member] \| Four Point Five Percent Senior Notes Due Twenty Twenty Four [Member]
Debt Instrument [Line Items]
Liabilities Subject To Compromise, Long-term Debt	303.4
Debtor-in-Possession Financing, Interest Rate on Borrowings Outstanding		4.50%
Senior Notes [Member] \| Four Point Seven Five Percent Senior Notes Due Twenty Twenty Four [Member]
Debt Instrument [Line Items]
Liabilities Subject To Compromise, Long-term Debt	318.6
Debtor-in-Possession Financing, Interest Rate on Borrowings Outstanding		4.75%
Senior Notes [Member] \| Eight Point Zero Percent Senior Notes Due Twenty Twenty Four [Member]
Debt Instrument [Line Items]
Liabilities Subject To Compromise, Long-term Debt	292.3
Debtor-in-Possession Financing, Interest Rate on Borrowings Outstanding		8.00%
Senior Notes [Member] \| Five Point Two Zero Percent Senior Notes Due Twenty Twenty Five [Member]
Debt Instrument [Line Items]
Liabilities Subject To Compromise, Long-term Debt	333.7
Debtor-in-Possession Financing, Interest Rate on Borrowings Outstanding		5.20%
Senior Notes [Member] \| Seven Point Three Seven Five Senior Notes Due Twenty Twenty Five [Member]
Debt Instrument [Line Items]
Liabilities Subject To Compromise, Long-term Debt	360.8
Debtor-in-Possession Financing, Interest Rate on Borrowings Outstanding		7.375%
Senior Notes [Member] \| Seven Point Seven Five Percent Senior Notes Due Twenty Twenty Six [Member]
Debt Instrument [Line Items]
Liabilities Subject To Compromise, Long-term Debt	1,000.0
Debtor-in-Possession Financing, Interest Rate on Borrowings Outstanding		7.75%
Senior Notes [Member] \| Seven Point Two Zero Percent Debentures Due Twenty Twenty Seven [Member]
Debt Instrument [Line Items]
Liabilities Subject To Compromise, Long-term Debt	112.1
Debtor-in-Possession Financing, Interest Rate on Borrowings Outstanding		7.20%
Senior Notes [Member] \| Seven Point Eight Seven Five Percent Senior Notes Due Twenty Forty [Member]
Debt Instrument [Line Items]
Liabilities Subject To Compromise, Long-term Debt	300.0
Debtor-in-Possession Financing, Interest Rate on Borrowings Outstanding		7.875%
Senior Notes [Member] \| Five Point Four Zero Percent Senior Notes Due Twenty Forty Two [Member]
Debt Instrument [Line Items]
Liabilities Subject To Compromise, Long-term Debt	400.0
Debtor-in-Possession Financing, Interest Rate on Borrowings Outstanding		5.40%
Senior Notes [Member] \| Five Point Seven Five Percent Senior Notes Due Twenty Forty Four [Member]
Debt Instrument [Line Items]
Liabilities Subject To Compromise, Long-term Debt	1,000.5
Debtor-in-Possession Financing, Interest Rate on Borrowings Outstanding		5.75%
Senior Notes [Member] \| Five Point Eight Five Percent Senior Notes Due Twenty Forty Four [Member]
Debt Instrument [Line Items]
Liabilities Subject To Compromise, Long-term Debt	400.0
Debtor-in-Possession Financing, Interest Rate on Borrowings Outstanding		5.85%
Line of Credit [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Liabilities Subject To Compromise, Long-term Debt	$ 581.0