Accumulated Other Comprehensive Income (Loss), Net of Tax (Changes of AOCI) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	$ (515)	$ (455)	$ (550)	$ (350)	$ (350)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	59	(48)	77	(166)
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	243	10	260	23
Other Comprehensive Income (Loss), net of tax	302	(38)	337	(143)
Accumulated Other Comprehensive Income (Loss), Ending Balance	(213)	(493)	(213)	(493)	(550)
Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	7	(5)	(3)	(6)	(6)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	13	0	23	0	0
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(2)	1	(2)	2	3
Other Comprehensive Income (Loss), net of tax	11	1	21	2
Accumulated Other Comprehensive Income (Loss), Ending Balance	18	(4)	18	(4)	(3)
Pension and OPEB Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	(419)	(354)	(426)	(355)	(355)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	82	0	82	0
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	240	0	247	1
Other Comprehensive Income (Loss), net of tax	322	0	329	1
Accumulated Other Comprehensive Income (Loss), Ending Balance	(97)	(354)	(97)	(354)	(426)
Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	(103)	(96)	(121)	11	11
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(36)	(48)	(28)	(166)
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	5	9	15	20
Other Comprehensive Income (Loss), net of tax	(31)	(39)	(13)	(146)
Accumulated Other Comprehensive Income (Loss), Ending Balance	$ (134)	$ (135)	$ (134)	$ (135)	$ (121)