Accumulated Other Comprehensive Income (Loss), Net of Tax - Schedule of Changes in Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	$ (179)	$ (550)	$ (350)
Other Comprehensive Income (Loss) before Reclassifications	43	146	(230)
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	3	225	30
Net Current Period Other Comprehensive Income (Loss)	46	371	(200)
Accumulated Other Comprehensive Income (Loss), Ending Balance	(133)	(179)	(550)
Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	3	(3)	(6)
Other Comprehensive Income (Loss) before Reclassifications	42	9	0
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(9)	(3)	3
Net Current Period Other Comprehensive Income (Loss)	33	6	3
Accumulated Other Comprehensive Income (Loss), Ending Balance	36	3	(3)
Pension and OPEB Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	(102)	(426)	(355)
Other Comprehensive Income (Loss) before Reclassifications	19	76	(72)
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	7	248	1
Net Current Period Other Comprehensive Income (Loss)	26	324	(71)
Accumulated Other Comprehensive Income (Loss), Ending Balance	(76)	(102)	(426)
Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	(80)	(121)	11
Other Comprehensive Income (Loss) before Reclassifications	(18)	61	(158)
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	5	(20)	26
Net Current Period Other Comprehensive Income (Loss)	(13)	41	(132)
Accumulated Other Comprehensive Income (Loss), Ending Balance	$ (93)	$ (80)	$ (121)