Accumulated Other Comprehensive Income Reclassifications out of AOCI (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Balance	$ 194	$ 353	$ 98
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	67	(163)	251
Reclassification AOCI, Tax	9	(1)	(1)
Balance	234	194	353
Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent	21	56	81
Amortization of net gain
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive Income	(36)
Amortization of prior service credits
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive Income		6
Settlement (gain) lossa
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive Income		(1)	(1)
Equity Method Investments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Balance	9	(3)	(3)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(1)	12	0
Reclassification AOCI, Tax	0	0	0
Balance	8	9	(3)
Equity Method Investments | Amortization of net gain
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive Income	0
Equity Method Investments | Amortization of prior service credits
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive Income		0
Equity Method Investments | Settlement (gain) lossa
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive Income		0	0
Pension and Retiree Health and Welfare Benefit Items
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Balance	185	356	101
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	68	(175)	251
Reclassification AOCI, Tax	9	(1)	(1)
Balance	226	185	356
Pension and Retiree Health and Welfare Benefit Items | Amortization of net gain
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive Income	$ (36)
Pension and Retiree Health and Welfare Benefit Items | Amortization of prior service credits
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive Income		6
Pension and Retiree Health and Welfare Benefit Items | Settlement (gain) lossa
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive Income		$ (1)	$ (1)