Pension and Postretirement Benefit Plans - Components of net periodic benefit cost and other information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Non-operating expense
Total net periodic benefit cost (benefit)	$ (80)	$ (40)	$ (239)	$ (116)
Postretirement Benefits
Operating expense
Service cost	12	11	35	33
Non-operating expense
Interest cost	11	16	33	48
Expected return on plan assets	(19)	(20)	(58)	(60)
Amortization of transition asset	0	0	0	0
Amortization of prior service benefit	(9)	(8)	(25)	(24)
Amortization of net actuarial loss	14	11	42	34
Settlements, curtailments, special termination benefits and other	0	1	2	3
Total non-operating expense (benefit)	(3)	0	(6)	1
Total net periodic benefit cost (benefit)	9	11	29	34
United States | Qualified and Non-qualified Pension Benefits
Operating expense
Service cost	72	66	216	197
Non-operating expense
Interest cost	90	124	270	373
Expected return on plan assets	(264)	(263)	(792)	(786)
Amortization of transition asset	0	0	0	0
Amortization of prior service benefit	(6)	(6)	(18)	(18)
Amortization of net actuarial loss	132	123	396	368
Settlements, curtailments, special termination benefits and other	0	0	0	0
Total non-operating expense (benefit)	(48)	(22)	(144)	(63)
Total net periodic benefit cost (benefit)	24	44	72	134
International | Qualified and Non-qualified Pension Benefits
Operating expense
Service cost	41	39	125	115
Non-operating expense
Interest cost	25	31	75	95
Expected return on plan assets	(81)	(77)	(244)	(232)
Amortization of transition asset	1	1	2	2
Amortization of prior service benefit	0	(1)	(2)	(4)
Amortization of net actuarial loss	26	28	80	85
Settlements, curtailments, special termination benefits and other	0	0	0	0
Total non-operating expense (benefit)	(29)	(18)	(89)	(54)
Total net periodic benefit cost (benefit)	$ 12	$ 21	$ 36	$ 61