Long-Term Debt (Schedule Of Secured And Unsecured Debt) (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2021	Dec. 31, 2020	Apr. 30, 2021
Successor [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 6,790		$ 6,794
Weighted average interest rate	5.657%
Unamortized fair value adjustment	$ 232
Carrying amount of Total debt	7,022
Successor [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 5,935
Successor [Member] | Secured Debt [Member] | Term Loan Due 10/8/2027 [Member]
Debt Instrument [Line Items]
Maturity date	Oct. 08, 2027
Principal Outstanding	$ 1,471
Interest rate	4.50%
Successor [Member] | Secured Debt [Member] | First Lien Notes Due 10/15/2027 [Member]
Debt Instrument [Line Items]
Maturity date	Oct. 15, 2027
Principal Outstanding	$ 1,150
Interest rate	5.875%
Successor [Member] | Secured Debt [Member] | First Lien Notes Due 5/1/2028 [Member]
Debt Instrument [Line Items]
Maturity date	May 01, 2028
Principal Outstanding	$ 1,550
Interest rate	5.00%
Successor [Member] | Secured Debt [Member] | Second Lien Notes Due 5/1/2029 [Member]
Debt Instrument [Line Items]
Maturity date	May 01, 2029
Principal Outstanding	$ 1,000
Interest rate	6.75%
Successor [Member] | Secured Debt [Member] | Takeback Notes Due 11/1/2029 [Member]
Debt Instrument [Line Items]
Maturity date	Nov. 01, 2029
Principal Outstanding	$ 750
Interest rate	5.875%
Successor [Member] | Secured Debt [Member] | IDRB Due 5/1/2030 [Member]
Debt Instrument [Line Items]
Maturity date	May 01, 2030
Principal Outstanding	$ 14
Interest rate	6.20%
Successor [Member] | Secured Subsidiary Debt [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 105
Successor [Member] | Secured Subsidiary Debt [Member] | Debentures Due 11/15/2031 [Member]
Debt Instrument [Line Items]
Maturity date	Nov. 15, 2031
Principal Outstanding	$ 100
Interest rate	8.50%
Successor [Member] | Secured Subsidiary Debt [Member] | RUS Loan Contracts Due 1/3/2028 [Member]
Debt Instrument [Line Items]
Maturity date	Jan. 03, 2028
Principal Outstanding	$ 5
Interest rate	6.154%
Successor [Member] | Unsecured Subsidiary Debt [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 750
Successor [Member] | Unsecured Subsidiary Debt [Member] | Debentures Due 5/15/2027 [Member]
Debt Instrument [Line Items]
Maturity date	May 15, 2027
Principal Outstanding	$ 200
Interest rate	6.75%
Successor [Member] | Unsecured Subsidiary Debt [Member] | Debentures Due 2/1/2028 [Member]
Debt Instrument [Line Items]
Maturity date	Feb. 01, 2028
Principal Outstanding	$ 300
Interest rate	6.86%
Successor [Member] | Unsecured Subsidiary Debt [Member] | Debentures Due 2/15/2028 [Member]
Debt Instrument [Line Items]
Maturity date	Feb. 15, 2028
Principal Outstanding	$ 200
Interest rate	6.73%
Successor [Member] | Unsecured Subsidiary Debt [Member] | Debentures Due 10/15/2029 [Member]
Debt Instrument [Line Items]
Maturity date	Oct. 15, 2029
Principal Outstanding	$ 50
Interest rate	8.40%
Successor [Member] | Total Debt [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 6,790
Weighted average interest rate	5.657%
Predecessor [Member]
Debt Instrument [Line Items]
Principal Outstanding		$ 16,769	$ 6,794
Less: Debt subject to compromise		(10,949)
Carrying amount of Total debt		5,820
Predecessor [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Principal Outstanding		$ 4,964
Predecessor [Member] | Secured Debt [Member] | Term Loan Due 10/8/2027 [Member]
Debt Instrument [Line Items]
Maturity date		Oct. 08, 2027
Principal Outstanding		$ 1,250
Interest rate		5.75%
Predecessor [Member] | Secured Debt [Member] | First Lien Notes Due 10/15/2027 [Member]
Debt Instrument [Line Items]
Maturity date		Oct. 15, 2027
Principal Outstanding		$ 1,150
Interest rate		5.875%
Predecessor [Member] | Secured Debt [Member] | First Lien Notes Due 5/1/2028 [Member]
Debt Instrument [Line Items]
Maturity date		May 01, 2028
Principal Outstanding		$ 1,550
Interest rate		5.00%
Predecessor [Member] | Secured Debt [Member] | Second Lien Notes Due 5/1/2029 [Member]
Debt Instrument [Line Items]
Maturity date		May 01, 2029
Principal Outstanding		$ 1,000
Interest rate		6.75%
Predecessor [Member] | Secured Debt [Member] | IDRB Due 5/1/2030 [Member]
Debt Instrument [Line Items]
Maturity date		May 01, 2030
Principal Outstanding		$ 14
Interest rate		6.20%
Predecessor [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Principal Outstanding		$ 10,949
Predecessor [Member] | Unsecured Debt [Member] | Senior Note Due 4/15/2020 [Member]
Debt Instrument [Line Items]
Maturity date		Apr. 15, 2020
Principal Outstanding		$ 172
Interest rate		8.50%
Predecessor [Member] | Unsecured Debt [Member] | Senior Note Due 9/15/2020 [Member]
Debt Instrument [Line Items]
Maturity date		Sep. 15, 2020
Principal Outstanding		$ 55
Interest rate		8.875%
Predecessor [Member] | Unsecured Debt [Member] | Senior Note Due 7/1/2021 [Member]
Debt Instrument [Line Items]
Maturity date		Jul. 01, 2021
Principal Outstanding		$ 89
Interest rate		9.25%
Predecessor [Member] | Unsecured Debt [Member] | Senior Note Due 9/15/2021 [Member]
Debt Instrument [Line Items]
Maturity date		Sep. 15, 2021
Principal Outstanding		$ 220
Interest rate		6.25%
Predecessor [Member] | Unsecured Debt [Member] | Senior Note Due 4/15/2022 [Member]
Debt Instrument [Line Items]
Maturity date		Apr. 15, 2022
Principal Outstanding		$ 500
Interest rate		8.75%
Predecessor [Member] | Unsecured Debt [Member] | Senior Note Due 9/15/2022 [Member]
Debt Instrument [Line Items]
Maturity date		Sep. 15, 2022
Principal Outstanding		$ 2,188
Interest rate		10.50%
Predecessor [Member] | Unsecured Debt [Member] | Senior Note Due 1/15/2023 [Member]
Debt Instrument [Line Items]
Maturity date		Jan. 15, 2023
Principal Outstanding		$ 850
Interest rate		7.125%
Predecessor [Member] | Unsecured Debt [Member] | Senior Note Due 4/15/2024 [Member]
Debt Instrument [Line Items]
Maturity date		Apr. 15, 2024
Principal Outstanding		$ 750
Interest rate		7.625%
Predecessor [Member] | Unsecured Debt [Member] | Senior Note Due 1/15/2025 [Member]
Debt Instrument [Line Items]
Maturity date		Jan. 15, 2025
Principal Outstanding		$ 775
Interest rate		6.875%
Predecessor [Member] | Unsecured Debt [Member] | Senior Note Due 9/15/2025 [Member]
Debt Instrument [Line Items]
Maturity date		Sep. 15, 2025
Principal Outstanding		$ 3,600
Interest rate		11.00%
Predecessor [Member] | Unsecured Debt [Member] | Debentures Due 11/1/2025 [Member]
Debt Instrument [Line Items]
Maturity date		Nov. 01, 2025
Principal Outstanding		$ 138
Interest rate		7.00%
Predecessor [Member] | Unsecured Debt [Member] | Debentures Due 8/15/2026 [Member]
Debt Instrument [Line Items]
Maturity date		Aug. 15, 2026
Principal Outstanding		$ 2
Interest rate		6.80%
Predecessor [Member] | Unsecured Debt [Member] | Senior Note Due 1/15/2027 [Member]
Debt Instrument [Line Items]
Maturity date		Jan. 15, 2027
Principal Outstanding		$ 346
Interest rate		7.875%
Predecessor [Member] | Unsecured Debt [Member] | Senior Note Due 8/15/2031 [Member]
Debt Instrument [Line Items]
Maturity date		Aug. 15, 2031
Principal Outstanding		$ 945
Interest rate		9.00%
Predecessor [Member] | Unsecured Debt [Member] | Debentures Due 10/1/2034 [Member]
Debt Instrument [Line Items]
Maturity date		Oct. 01, 2034
Principal Outstanding		$ 1
Interest rate		7.68%
Predecessor [Member] | Unsecured Debt [Member] | Debentures Due 7/1/2035 [Member]
Debt Instrument [Line Items]
Maturity date		Jul. 01, 2035
Principal Outstanding		$ 125
Interest rate		7.45%
Predecessor [Member] | Unsecured Debt [Member] | Debentures Due 10/1/2046 [Member]
Debt Instrument [Line Items]
Maturity date		Oct. 01, 2046
Principal Outstanding		$ 193
Interest rate		7.05%
Predecessor [Member] | Secured Subsidiary Debt [Member]
Debt Instrument [Line Items]
Principal Outstanding		$ 106
Predecessor [Member] | Secured Subsidiary Debt [Member] | Debentures Due 11/15/2031 [Member]
Debt Instrument [Line Items]
Maturity date		Nov. 15, 2031
Principal Outstanding		$ 100
Interest rate		8.50%
Predecessor [Member] | Secured Subsidiary Debt [Member] | RUS Loan Contracts Due 1/3/2028 [Member]
Debt Instrument [Line Items]
Maturity date		Jan. 03, 2028
Principal Outstanding		$ 6
Interest rate		6.154%
Predecessor [Member] | Unsecured Subsidiary Debt [Member]
Debt Instrument [Line Items]
Principal Outstanding		$ 750
Predecessor [Member] | Unsecured Subsidiary Debt [Member] | Debentures Due 5/15/2027 [Member]
Debt Instrument [Line Items]
Maturity date		May 15, 2027
Principal Outstanding		$ 200
Interest rate		6.75%
Predecessor [Member] | Unsecured Subsidiary Debt [Member] | Debentures Due 2/1/2028 [Member]
Debt Instrument [Line Items]
Maturity date		Feb. 01, 2028
Principal Outstanding		$ 300
Interest rate		6.86%
Predecessor [Member] | Unsecured Subsidiary Debt [Member] | Debentures Due 2/15/2028 [Member]
Debt Instrument [Line Items]
Maturity date		Feb. 15, 2028
Principal Outstanding		$ 200
Interest rate		6.73%
Predecessor [Member] | Unsecured Subsidiary Debt [Member] | Debentures Due 10/15/2029 [Member]
Debt Instrument [Line Items]
Maturity date		Oct. 15, 2029
Principal Outstanding		$ 50
Interest rate		8.40%
Predecessor [Member] | Total Debt [Member]
Debt Instrument [Line Items]
Principal Outstanding		$ 16,769
Weighted average interest rate		8.188%