Employee Benefits - Costs (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Pension Benefits
Net Periodic Benefit Cost
Net Periodic Other Benefit Costs	$ 231	$ 369	$ 1,006	$ 856
Pension Benefits | United States
Net Periodic Benefit Cost
Service cost	112	124	337	373
Interest cost	56	89	175	265
Expected return on plan assets	(145)	(163)	(439)	(488)
Amortization of prior service costs (credits)	0	0	1	1
Amortization of actuarial losses (gains)	68	96	245	288
Settlement losses	108	184	576	304
Net Periodic Other Benefit Costs	199	330	895	743
Pension Benefits | International
Net Periodic Benefit Cost
Service cost	27	33	98	97
Interest cost	35	44	104	131
Expected return on plan assets	(42)	(52)	(131)	(155)
Amortization of prior service costs (credits)	2	2	6	7
Amortization of actuarial losses (gains)	11	12	35	33
Settlement losses	(1)	0	(1)	0
Net Periodic Other Benefit Costs	32	39	111	113
Other Benefits
Net Periodic Benefit Cost
Service cost	11	9	32	28
Interest cost	15	18	41	53
Amortization of prior service costs (credits)	(7)	(7)	(20)	(21)
Amortization of actuarial losses (gains)	3	1	11	3
Net Periodic Other Benefit Costs	$ 22	$ 21	$ 64	$ 63