Pension and Postretirement Benefit Plans - Components of net periodic benefit cost and other information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Net periodic benefit cost (benefit)
Net periodic benefit cost (benefit)	$ (80)	$ (38)	$ (159)	$ (76)
Funded | Postretirement Benefits
Net periodic benefit cost (benefit)
Service cost	11	11	23	22
Interest cost	11	16	22	32
Expected return on plan assets	(20)	(20)	(39)	(40)
Amortization of prior service benefit	(8)	(8)	(16)	(16)
Amortization of net actuarial loss	14	11	28	23
Settlements, curtailments, special terminations and other	1	1	2	2
Total non-operating expense (benefit)	(2)		(3)	1
Net periodic benefit cost (benefit)	9	11	20	23
Funded | United States | Qualified and Non-qualified Pension Benefits
Net periodic benefit cost (benefit)
Service cost	72	65	144	131
Interest cost	90	125	180	249
Expected return on plan assets	(264)	(261)	(528)	(523)
Amortization of prior service benefit	(6)	(6)	(12)	(12)
Amortization of net actuarial loss	132	122	264	245
Total non-operating expense (benefit)	(48)	(20)	(96)	(41)
Net periodic benefit cost (benefit)	24	45	48	90
Funded | International | Qualified and Non-qualified Pension Benefits
Net periodic benefit cost (benefit)
Service cost	42	38	84	76
Interest cost	25	33	50	64
Expected return on plan assets	(82)	(78)	(163)	(155)
Amortization of transition asset	1		1	1
Amortization of prior service benefit	(1)	(2)	(2)	(3)
Amortization of net actuarial loss	27	29	54	57
Total non-operating expense (benefit)	(30)	(18)	(60)	(36)
Net periodic benefit cost (benefit)	$ 12	$ 20	$ 24	$ 40