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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Net periodic benefit cost (benefit)
Net periodic benefit cost (benefit)	$ (19)	$ (38)	$ (53)	$ (73)
Funded | Postretirement Benefits
Net periodic benefit cost (benefit)
Service cost	11	10	33	32
Interest cost	16	20	48	62
Expected return on plan assets	(20)	(20)	(60)	(61)
Amortization of prior service benefit	(8)	(9)	(24)	(23)
Amortization of net actuarial loss	12	8	36	25
Settlements, curtailments, special terminations and other	1		3
Total non-operating expense (benefit)	1	(1)	3	3
Net periodic benefit cost (benefit)	12	9	36	35
Funded | United States | Qualified and Non-qualified Pension Benefits
Net periodic benefit cost (benefit)
Service cost	66	63	197	188
Interest cost	124	155	374	466
Expected return on plan assets	(255)	(260)	(765)	(780)
Amortization of prior service benefit	(6)	(6)	(18)	(18)
Amortization of net actuarial loss	134	91	402	274
Settlements, curtailments, special terminations and other				35
Total non-operating expense (benefit)	(3)	(20)	(7)	(23)
Net periodic benefit cost (benefit)	63	43	190	165
Funded | International | Qualified and Non-qualified Pension Benefits
Net periodic benefit cost (benefit)
Service cost	39	32	115	98
Interest cost	31	40	95	118
Expected return on plan assets	(77)	(75)	(231)	(225)
Amortization of transition asset	1		2
Amortization of prior service benefit	(1)	(3)	(4)	(9)
Amortization of net actuarial loss	30	20	92	59
Settlements, curtailments, special terminations and other				1
Total non-operating expense (benefit)	(16)	(18)	(46)	(56)
Net periodic benefit cost (benefit)	$ 23	$ 14	$ 69	$ 42