Comprehensive Income (Loss) (Accumulated Other Comprehensive Income (Loss), Net Of Tax) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Jan. 01, 2022	Jan. 01, 2021
Successor [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning	$ 4,600
Net current-period other comprehensive income (loss)	(2)
Balance at ending	4,678
Successor [Member] | Pension And OPEB [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax	15
Successor [Member] | Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning	60
Other comprehensive income (loss) before reclassifications	1
Amounts reclassified from accumulated other comprehensive income (loss) to net loss	(3)
Net current-period other comprehensive income (loss)	(2)
Balance at ending	58
Successor [Member] | Accumulated Other Comprehensive Income (Loss) [Member] | OPEB [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning	60
Other comprehensive income (loss) before reclassifications	1
Amounts reclassified from accumulated other comprehensive income (loss) to net loss	(3)
Net current-period other comprehensive income (loss)	(2)
Balance at ending	$ 58
Predecessor [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning		$ (4,900)
Net current-period other comprehensive income (loss)		11
Balance at ending		(4,830)
Predecessor [Member] | Pension And OPEB [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax		230	$ 15	$ 234
Predecessor [Member] | Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning		(755)
Amounts reclassified from accumulated other comprehensive income (loss) to net loss		11
Net current-period other comprehensive income (loss)		11
Balance at ending		(744)
Predecessor [Member] | Accumulated Other Comprehensive Income (Loss) [Member] | Pension [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning		(699)
Amounts reclassified from accumulated other comprehensive income (loss) to net loss		14
Net current-period other comprehensive income (loss)		14
Balance at ending		(685)
Predecessor [Member] | Accumulated Other Comprehensive Income (Loss) [Member] | OPEB [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning		(56)
Amounts reclassified from accumulated other comprehensive income (loss) to net loss		(3)
Net current-period other comprehensive income (loss)		(3)
Balance at ending		$ (59)