Comprehensive Income (Loss) (Reclassification Out Of AOCI) (Details) - Reclassification Out Of Accumulated Other Comprehensive Income [Member] - USD ($) $ in Millions	4 Months Ended	8 Months Ended	12 Months Ended
	Apr. 30, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Successor [Member] | OPEB [Member] | Amortization Of Defined Benefit Cost Items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax		$ 5
Tax impact		(1)
Reclassifications, net of tax		4
Successor [Member] | OPEB [Member] | Prior-Service Credits (Costs) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax		$ 5
Predecessor [Member] | Pension [Member] | Amortization Of Defined Benefit Cost Items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax	$ (24)		$ (339)	$ (115)
Tax impact	5		34	26
Reclassifications, net of tax	(19)		(305)	(89)
Predecessor [Member] | Pension [Member] | Actuarial Gains (Losses) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax	(24)		(99)	(58)
Predecessor [Member] | Pension [Member] | Loss On Disposal [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax			(81)
Predecessor [Member] | Pension [Member] | Pension Settlement Cost [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax			(159)	(57)
Reclassifications, net of tax			122	43
Predecessor [Member] | OPEB [Member] | Amortization Of Defined Benefit Cost Items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax	5		19	15
Tax impact	(1)		(5)	(2)
Reclassifications, net of tax	4		14	13
Predecessor [Member] | OPEB [Member] | Prior-Service Credits (Costs) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax	10		32	11
Predecessor [Member] | OPEB [Member] | Actuarial Gains (Losses) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax	$ (5)		(6)	$ 4
Predecessor [Member] | OPEB [Member] | Loss On Disposal [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax			$ (7)