Accumulated Other Comprehensive Income (Loss), Net of Tax (Changes of AOCI) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	$ (350)	$ (504)	$ (504)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(65)	(40)
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	5	2
Other Comprehensive Income (Loss), net of tax	(60)	(38)
Accumulated Other Comprehensive Income (Loss), Ending Balance	(410)	(542)	(350)
Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	(6)	(9)	(9)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	0	0
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	1	1	3
Other Comprehensive Income (Loss), net of tax	1	1
Accumulated Other Comprehensive Income (Loss), Ending Balance	(5)	(8)	(6)
Pension and OPEB Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	(355)	(545)	(545)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	0
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	0	3
Other Comprehensive Income (Loss), net of tax	0	3
Accumulated Other Comprehensive Income (Loss), Ending Balance	(355)	(542)	(355)
Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	11	50	50
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(65)	(40)
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	4	(2)
Other Comprehensive Income (Loss), net of tax	(61)	(42)
Accumulated Other Comprehensive Income (Loss), Ending Balance	$ (50)	$ 8	$ 11