Employee Benefit Plans - Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Changes Recognized in Comprehensive Income
Net actuarial (gain) loss during period	$ 2,004	$ 2,404	$ (85)
Amortization of actuarial loss	(1,107)	(519)	(792)
Prior service (credits) costs during period	0	28	26
Amortization of prior service (costs) credits	23	(4)	13
Other Benefits
Net Periodic Benefit Cost
Service cost	38	36	42
Interest cost	71	96	94
Expected return on plan assets	0	0	0
Amortization of prior service costs (credits)	(28)	(28)	(28)
Recognized actuarial losses	3	(3)	15
Settlement losses	0	0	0
Curtailment losses (gains)	(27)	0	0
Total net periodic benefit cost	57	101	123
Changes Recognized in Comprehensive Income
Net actuarial (gain) loss during period	190	128	(248)
Amortization of actuarial loss	(4)	3	(15)
Prior service (credits) costs during period	0	(1)	3
Amortization of prior service (costs) credits	42	28	28
Total changes recognized in other comprehensive income	228	158	(232)
Recognized in Net Periodic Benefit Cost and Other Comprehensive Income	285	259	(109)
U.S. \| Pension Benefits
Net Periodic Benefit Cost
Service cost	497	406	480
Interest cost	353	397	370
Expected return on plan assets	(650)	(565)	(636)
Amortization of prior service costs (credits)	2	2	2
Recognized actuarial losses	385	239	304
Settlement losses	620	259	411
Curtailment losses (gains)	92	0	0
Total net periodic benefit cost	1,299	738	931
Changes Recognized in Comprehensive Income
Net actuarial (gain) loss during period	1,584	1,939	151
Amortization of actuarial loss	(1,005)	(498)	(715)
Prior service (credits) costs during period	0	0	0
Amortization of prior service (costs) credits	(2)	(2)	(2)
Total changes recognized in other comprehensive income	577	1,439	(566)
Recognized in Net Periodic Benefit Cost and Other Comprehensive Income	1,876	2,177	365
Int’l. \| Pension Benefits
Net Periodic Benefit Cost
Service cost	130	139	141
Interest cost	175	199	206
Expected return on plan assets	(209)	(231)	(253)
Amortization of prior service costs (credits)	10	11	10
Recognized actuarial losses	45	21	29
Settlement losses	37	3	33
Curtailment losses (gains)	2	16	3
Total net periodic benefit cost	190	158	169
Changes Recognized in Comprehensive Income
Net actuarial (gain) loss during period	230	338	12
Amortization of actuarial loss	(98)	(24)	(62)
Prior service (credits) costs during period	0	29	23
Amortization of prior service (costs) credits	(17)	(30)	(13)
Total changes recognized in other comprehensive income	115	313	(40)
Recognized in Net Periodic Benefit Cost and Other Comprehensive Income	$ 305	$ 471	$ 129

Amount recognized in net periodic benefit cost (credit) and other comprehensive (income) loss.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of gain (loss), recognized immediately as component of net periodic benefit (cost) credit, for change in value of benefit obligation or plan assets from experience different from that assumed, change in actuarial assumption, or consequence of temporarily deviating from substantive plan. Includes, but is not limited to, amount in excess of ten percent of greater of fair value of plan assets or benefit obligation.