Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other net periodic benefit credits	$ 5			$ 5			$ 11	$ 14
Provision (benefit) for income taxes	127			240			314	2
Net income	453	$ 287	$ 417	817	$ 966	$ 1,304	1,157	3,087
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	4			4			11	11
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			16	16
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	0			0			(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)			$ (3)	$ (3)