Chapter 11 Proceedings and Ability to Continue as a Going Concern - Schedule of Liabilities Subject to Compromise (Details) - USD ($) $ in Millions	Jun. 30, 2021	Apr. 30, 2021	Dec. 31, 2020	Aug. 18, 2020	Jun. 30, 2020
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	$ 0.0	$ 0.0	7,313.7		$ 7,313.7
Senior Notes \| Six Point Eight Seven Five Percent Senior Notes Due Two Thousand Twenty Member
Debt Instrument [Line Items]
Long-term debt			122.9
Interest rate on borrowings outstanding				6.875%
Senior Notes \| Four Point Seven Zero Percent Senior Notes Due Twenty Twenty One [Member]
Debt Instrument [Line Items]
Long-term debt			100.7
Interest rate on borrowings outstanding				4.70%
Senior Notes \| Four Point Eight Seven Five Percent Senior Notes Due Twenty Twenty Two [Member]
Debt Instrument [Line Items]
Long-term debt			620.8
Interest rate on borrowings outstanding				4.875%
Senior Notes \| Three Point Zero Percent Exchangeable Senior Notes Due Twenty Twenty Four [Member]
Debt Instrument [Line Items]
Long-term debt			849.5
Interest rate on borrowings outstanding				3.00%
Senior Notes \| Four Point Five Percent Senior Notes Due Twenty Twenty Four [Member]
Debt Instrument [Line Items]
Long-term debt			303.4
Interest rate on borrowings outstanding				4.50%
Senior Notes \| Four Point Seven Five Percent Senior Notes Due Twenty Twenty Four [Member]
Debt Instrument [Line Items]
Long-term debt			318.6
Interest rate on borrowings outstanding				4.75%
Senior Notes \| Eight Point Zero Percent Senior Notes Due Twenty Twenty Four [Member]
Debt Instrument [Line Items]
Long-term debt			292.3
Interest rate on borrowings outstanding				8.00%
Senior Notes \| Five Point Two Zero Percent Senior Notes Due Twenty Twenty Five [Member]
Debt Instrument [Line Items]
Long-term debt			333.7
Interest rate on borrowings outstanding				5.20%
Senior Notes \| Seven Point Three Seven Five Senior Notes Due Twenty Twenty Five [Member]
Debt Instrument [Line Items]
Long-term debt			360.8
Interest rate on borrowings outstanding				7.375%
Senior Notes \| Seven Point Seven Five Percent Senior Notes Due Twenty Twenty Six [Member]
Debt Instrument [Line Items]
Long-term debt			1,000.0
Interest rate on borrowings outstanding				7.75%
Senior Notes \| Seven Point Two Zero Percent Debentures Due Twenty Twenty Seven [Member]
Debt Instrument [Line Items]
Long-term debt			112.1
Interest rate on borrowings outstanding				7.20%
Senior Notes \| Seven Point Eight Seven Five Percent Senior Notes Due Twenty Forty [Member]
Debt Instrument [Line Items]
Long-term debt			300.0
Interest rate on borrowings outstanding				7.875%
Senior Notes \| Five Point Four Zero Percent Senior Notes Due Twenty Forty Two [Member]
Debt Instrument [Line Items]
Long-term debt			400.0
Interest rate on borrowings outstanding				5.40%
Senior Notes \| Five Point Seven Five Percent Senior Notes Due Twenty Forty Four [Member]
Debt Instrument [Line Items]
Long-term debt			1,000.5
Interest rate on borrowings outstanding				5.75%
Senior Notes \| Five Point Eight Five Percent Senior Notes Due Twenty Forty Four [Member]
Debt Instrument [Line Items]
Long-term debt			400.0
Interest rate on borrowings outstanding				5.85%
Line of Credit \| Revolving Credit Facility
Debt Instrument [Line Items]
Long-term debt			$ 581.0