Accumulated Other Comprehensive Loss - Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Income tax provision (benefit)	$ (195)	$ (51)	$ (58)
Total reclassification, net of tax	307	10	(47)
Amounts Reclassified from Accumulated Other Comprehensive Loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Total reclassification, net of tax	51	50	10
Unamortized Prior Service Credits (Costs) | Amounts Reclassified from Accumulated Other Comprehensive Loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Income tax provision (benefit)	0	0	0
Total reclassification, net of tax	(4)	(17)	(12)
Unamortized Prior Service Credits (Costs) | Amounts Reclassified from Accumulated Other Comprehensive Loss | Non-operating pension and other postretirement benefit credits
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Amortization of prior service costs or credits	(3)	(4)	(11)
Curtailment gain	(1)	(13)	(1)
Unamortized Actuarial Losses | Amounts Reclassified from Accumulated Other Comprehensive Loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Other items	0	3	0
Income tax provision (benefit)	(17)	(21)	(7)
Total reclassification, net of tax	55	67	22
Unamortized Actuarial Losses | Amounts Reclassified from Accumulated Other Comprehensive Loss | Non-operating pension and other postretirement benefit credits
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Amortization of actuarial losses	72	57	28
Settlement loss	$ 0	$ 28	$ 1