Accumulated Other Comprehensive Income (Loss), Net of Tax (Changes of AOCI) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	$ (550)	$ (350)	$ (350)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	18	(65)
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	10	5
Other Comprehensive Income (Loss), net of tax	28	(60)
Accumulated Other Comprehensive Income (Loss), Ending Balance	(522)	(410)	(550)
Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	(3)	(6)	(6)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(2)	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	(4)	(5)	(3)
Pension and OPEB Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	(426)	(355)	(355)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	0
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	3	0
Other Comprehensive Income (Loss), net of tax	3	0
Accumulated Other Comprehensive Income (Loss), Ending Balance	(423)	(355)	(426)
Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	(121)	11	11
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	20	(65)
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	6	4
Other Comprehensive Income (Loss), net of tax	26	(61)
Accumulated Other Comprehensive Income (Loss), Ending Balance	$ (95)	$ (50)	$ (121)