Pension and Postretirement Benefit Plans - Components of net periodic benefit cost and other information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Net periodic benefit cost (benefit)
Net periodic benefit cost (benefit)	$ (79)	$ (38)
Funded | Postretirement Benefits
Net periodic benefit cost (benefit)
Service cost	12	11
Interest cost	11	16
Expected return on plan assets	(19)	(20)
Amortization of prior service benefit	(8)	(8)
Amortization of net actuarial loss	14	11
Settlements, curtailments, special terminations and other	1	1
Total non-operating expense (benefit)	(1)
Net periodic benefit cost (benefit)	11	11
Funded | United States | Qualified and Non-qualified Pension Benefits
Net periodic benefit cost (benefit)
Service cost	72	66
Interest cost	90	124
Expected return on plan assets	(264)	(262)
Amortization of prior service benefit	(6)	(6)
Amortization of net actuarial loss	132	123
Total non-operating expense (benefit)	(48)	(21)
Net periodic benefit cost (benefit)	24	45
Funded | International | Qualified and Non-qualified Pension Benefits
Net periodic benefit cost (benefit)
Service cost	42	38
Interest cost	25	31
Expected return on plan assets	(81)	(77)
Amortization of transition asset		1
Amortization of prior service benefit	(1)	(1)
Amortization of net actuarial loss	27	29
Total non-operating expense (benefit)	(30)	(17)
Net periodic benefit cost (benefit)	$ 12	$ 21