Pension and Other Postretirement Benefits - Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Pension benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 5	$ 6	$ 16	$ 16
Interest cost	15	27	48	81
Expected return on plan assets	(24)	(42)	(84)	(127)
Recognized net actuarial loss	19	31	75	92
Amortization of prior service benefit	0	0	0	(1)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	5	3	573	58
Net periodic benefit cost	20	25	628	119
Pension benefits | UNITED STATES
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Other Comprehensive Income (Loss), Defined Benefit Plan, Settlement and Curtailment Gain (Loss), before Tax			549
Defined Benefit Plan, Benefit Obligation, Payment for Settlement	5		24
Other postretirement benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	2	1	5	3
Interest cost	3	2	8	10
Recognized net actuarial loss	2	3	7	6
Amortization of prior service benefit	(2)	(1)	(5)	(2)
Net periodic benefit cost	$ 5	$ 5	$ 15	$ 17