Pension and Postretirement Benefit Plans and Defined Contribution Plans - Schedule of Net Periodic Benefit Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 38	$ 37	$ 39
Interest cost	49	75	72
Expected return on plan assets	(36)	(33)	(37)
Amortization of actuarial losses	0	3	7
Amortization of prior service credits/(credits)	(170)	(173)	(178)
Curtailments	0	(47)	(17)
Settlements	0	(10)	0
Special termination benefits	0	2	2
Net periodic benefit cost/(credit) reported in income	(118)	(146)	(111)
(Credit)/cost reported in Other comprehensive income/(loss)	(50)	38	105
(Credit)/cost recognized in Comprehensive income	(168)	(107)	(6)
International [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	146	125	136
Interest cost	164	215	212
Expected return on plan assets	(306)	(317)	(360)
Amortization of actuarial losses	125	80	101
Amortization of prior service credits/(credits)	(3)	(4)	(4)
Curtailments	0	(1)	(4)
Settlements	6	16	4
Special termination benefits	0	0	0
Net periodic benefit cost/(credit) reported in income	132	115	84
(Credit)/cost reported in Other comprehensive income/(loss)	202	570	84
(Credit)/cost recognized in Comprehensive income	333	685	168
Qualified Plan [Member] | US [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0
Interest cost	499	629	598
Expected return on plan assets	(1,015)	(890)	(1,040)
Amortization of actuarial losses	136	147	120
Amortization of prior service credits/(credits)	(3)	(3)	2
Curtailments	0	0	12
Settlements	223	230	113
Special termination benefits	(1)	4	6
Net periodic benefit cost/(credit) reported in income	(161)	116	(189)
(Credit)/cost reported in Other comprehensive income/(loss)	640	(246)	361
(Credit)/cost recognized in Comprehensive income	479	(129)	171
Non-Qualified Plan [Member] | US [Member] | U.S. Supplemental (Non-Qualified) Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0
Interest cost	34	47	55
Expected return on plan assets	0	0	0
Amortization of actuarial losses	15	11	13
Amortization of prior service credits/(credits)	(1)	(1)	(1)
Curtailments	0	0	1
Settlements	49	27	26
Special termination benefits	2	17	10
Net periodic benefit cost/(credit) reported in income	99	100	103
(Credit)/cost reported in Other comprehensive income/(loss)	95	115	(189)
(Credit)/cost recognized in Comprehensive income	$ 194	$ 215	$ (86)