Accumulated Other Comprehensive Income (Loss), Net of Tax (Changes of AOCI) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	$ (169)	$ (522)	$ (179)	$ (550)	$ (550)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(5)	0	3	18
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	1	7	3	17
Other Comprehensive Income (Loss), net of tax	(4)	7	6	35
Accumulated Other Comprehensive Income (Loss), Ending Balance	(173)	(515)	(173)	(515)	(179)
Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	21	(4)	3	(3)	(3)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	2	12	22	10	9
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(3)	(1)	(5)	0	(3)
Other Comprehensive Income (Loss), net of tax	(1)	11	17	10
Accumulated Other Comprehensive Income (Loss), Ending Balance	20	7	20	7	3
Pension and OPEB Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	(100)	(423)	(102)	(426)	(426)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	0	0	0
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	2	4	4	7
Other Comprehensive Income (Loss), net of tax	2	4	4	7
Accumulated Other Comprehensive Income (Loss), Ending Balance	(98)	(419)	(98)	(419)	(102)
Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	(90)	(95)	(80)	(121)	(121)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(7)	(12)	(19)	8
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	2	4	4	10
Other Comprehensive Income (Loss), net of tax	(5)	(8)	(15)	18
Accumulated Other Comprehensive Income (Loss), Ending Balance	$ (95)	$ (103)	$ (95)	$ (103)	$ (80)