Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2023	Jun. 30, 2022
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other net periodic benefit credits	$ 3		$ 5		$ 6	$ 9
Provision (benefit) for income taxes	78		279		187	(238)
Net income	287	$ 417	966	$ 1,304	704	2,270
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Total reclassifications of expense, net of tax
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income	3		3		7	7
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Amortization of prior service credit
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other net periodic benefit credits	5		5		11	11
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Amortization of actuarial loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other net periodic benefit credits	(1)		(1)		(1)	(2)
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Net settlement loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other net periodic benefit credits	0		0		(1)	0
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Income Tax
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Provision (benefit) for income taxes	$ (1)		$ (1)		$ (2)	$ (2)