Comprehensive Income (Loss) (Accumulated Other Comprehensive Income (Loss), Net Of Tax) (Details) - USD ($) $ in Millions	4 Months Ended	8 Months Ended	12 Months Ended
	Apr. 30, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Successor [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net current-period other comprehensive income (loss)		$ 60
Balance at ending		4,600
Successor [Member] | Pension And OPEB [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Deferred tax items		15
Successor [Member] | Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications		64
Amounts reclassified from accumulated other comprehensive income (loss) to net loss		(4)
Net current-period other comprehensive income (loss)		60
Balance at ending		60
Successor [Member] | Accumulated Other Comprehensive Income (Loss) [Member] | OPEB [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications		64
Amounts reclassified from accumulated other comprehensive income (loss) to net loss		(4)
Net current-period other comprehensive income (loss)		60
Balance at ending		60
Predecessor [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning	$ (4,900)	$ 4,108	$ (4,394)	$ 1,600
Net current-period other comprehensive income (loss)	359		(105)	(108)
Balance at ending	4,108		(4,900)	(4,394)
Predecessor [Member] | Pension And OPEB [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Deferred tax items			234	204	$ 250
Predecessor [Member] | Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning	(755)		(650)	(463)
Other comprehensive income (loss) before reclassifications	344		(396)	(184)
Amounts reclassified from accumulated other comprehensive income (loss) to net loss	15		291	76
Net current-period other comprehensive income (loss)	359		(105)	(108)
Cancellation of Predecessor equity	396
Balance at ending			(755)	(650)
Predecessor [Member] | Accumulated Other Comprehensive Income (Loss) [Member] | Accounting Standards Update 2018-02 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning			(79)
Balance at ending				(79)
Predecessor [Member] | Accumulated Other Comprehensive Income (Loss) [Member] | Pension [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning	(699)		(684)	(489)
Other comprehensive income (loss) before reclassifications	270		(320)	(201)
Amounts reclassified from accumulated other comprehensive income (loss) to net loss	19		305	89
Net current-period other comprehensive income (loss)	289		15	(112)
Cancellation of Predecessor equity	410
Balance at ending			(699)	(684)
Predecessor [Member] | Accumulated Other Comprehensive Income (Loss) [Member] | Pension [Member] | Accounting Standards Update 2018-02 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning			(83)
Balance at ending				(83)
Predecessor [Member] | Accumulated Other Comprehensive Income (Loss) [Member] | OPEB [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning	(56)		34	26
Other comprehensive income (loss) before reclassifications	74		(76)	17
Amounts reclassified from accumulated other comprehensive income (loss) to net loss	(4)		(14)	(13)
Net current-period other comprehensive income (loss)	70		(90)	4
Cancellation of Predecessor equity	$ (14)
Balance at ending			(56)	34
Predecessor [Member] | Accumulated Other Comprehensive Income (Loss) [Member] | OPEB [Member] | Accounting Standards Update 2018-02 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning			$ 4
Balance at ending				$ 4