Liquidity And Financial Condition (Narrative) (Details) - USD ($) $ in Millions								3 Months Ended
	Apr. 30, 2021	Mar. 01, 2021	Nov. 25, 2020	Oct. 08, 2020	Aug. 27, 2020	May 15, 2020	May 01, 2020	Mar. 31, 2021	Dec. 31, 2020
Reorganization [Line Items]
Unrestricted balance sheet excess cash		$ 150
Excess cash		$ 1,313
Principal Outstanding								$ 16,769	$ 16,769
JP Morgan Revolving Credit Facility [Member]
Reorganization [Line Items]
Maturity date								Feb. 27, 2024
Debt instrument, face amount								$ 850
JP Morgan Term Loan B [Member]
Reorganization [Line Items]
Maturity date								Jun. 15, 2024
Debt instrument, face amount								$ 1,740
Secured Debt [Member]
Reorganization [Line Items]
Principal Outstanding								4,964	4,964
Unsecured Debt [Member]
Reorganization [Line Items]
Principal Outstanding								10,949	10,949
Secured Subsidiary Debt [Member]
Reorganization [Line Items]
Principal Outstanding								106	106
Unsecured Subsidiary Debt [Member]
Reorganization [Line Items]
Takeback Debt, Principal amount					$ 750
Principal Outstanding								750	$ 750
Original First Lien Notes [Member]
Reorganization [Line Items]
Debt instrument, face amount				$ 1,650
Original Second Lien Notes [Member]
Reorganization [Line Items]
Interest rate			8.50%
Maturity date			Apr. 01, 2026
Debt instrument, face amount			$ 1,600
DIP Revolving Facility [Member]
Reorganization [Line Items]
DIP, Maximum line of credit				625		$ 460		$ 625
DIP Term Loan Facility [Member]
Reorganization [Line Items]
DIP, Maximum line of credit			$ 750	$ 500
Debenture Due 5/15/2027 [Member] | Unsecured Subsidiary Debt [Member]
Reorganization [Line Items]
Interest rate								6.75%
Maturity date								May 15, 2027
Debenture Due 2/1/2028 [Member] | Unsecured Subsidiary Debt [Member]
Reorganization [Line Items]
Interest rate								6.86%
Maturity date								Feb. 01, 2028
Debenture Due 2/15/2028 [Member] | Unsecured Subsidiary Debt [Member]
Reorganization [Line Items]
Interest rate								6.73%
Maturity date								Feb. 15, 2028
Debenture Due 10/15/2029 [Member] | Unsecured Subsidiary Debt [Member]
Reorganization [Line Items]
Interest rate								8.40%
Maturity date								Oct. 15, 2029
Debenture Due 11/15/2031 [Member] | Secured Subsidiary Debt [Member]
Reorganization [Line Items]
Interest rate								8.50%
Maturity date								Nov. 15, 2031
First Lien Secured Notes Due 10/15/27 [Member]
Reorganization [Line Items]
Interest rate				5.875%
Maturity date				Oct. 15, 2027
Principal Outstanding				$ 1,150
First Lien Notes Due May 2028 [Member]
Reorganization [Line Items]
Interest rate			5.00%
Maturity date			May 01, 2028
Principal Outstanding			$ 1,550
Second Lien Notes Due May 2029 [Member]
Reorganization [Line Items]
Interest rate			6.75%
Maturity date			May 01, 2029
Principal Outstanding			$ 1,000
Subsequent Event [Member] | Term Loan B [Member]
Reorganization [Line Items]
Payments to holders	$ 48
Subsequent Event [Member] | Original First Lien Notes [Member]
Reorganization [Line Items]
Payments to holders	9
Subsequent Event [Member] | Term Loan B, Second Payment [Member]
Reorganization [Line Items]
Payments to holders	$ 8
Maximum [Member]
Reorganization [Line Items]
Maturity period					8 years
Maximum [Member] | Secured Subsidiary Debt [Member]
Reorganization [Line Items]
Reorganization plan, Interest rate					2.50%
Maximum [Member] | Unsecured Subsidiary Debt [Member]
Reorganization [Line Items]
Reorganization plan, Interest rate					3.50%
Minimum [Member]
Reorganization [Line Items]
Maturity period					1 year
Minimum [Member] | Subsequent Event [Member]
Reorganization [Line Items]
Percentage of debt held by the Consenting Noteholders	50.10%
Northwest Operations [Member]
Reorganization [Line Items]
Net proceeds							$ 1,131
Net after-tax cash proceeds							$ 1,129