Employee Benefit Plans - Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Changes Recognized in Comprehensive Income
Prior service (credits) costs during period	$ 26	$ 1	$ (345)
Amortization of prior service (costs) credits	13	20	(19)
Other Benefits
Net Periodic Benefit Cost
Service cost	42	32	60
Interest cost	94	95	128
Expected return on plan assets	0	0	0
Amortization of prior service costs (credits)	(28)	(28)	14
Recognized actuarial losses	15	(5)	19
Settlement losses	0	0	0
Curtailment losses (gains)	0	0	0
Total net periodic benefit cost	123	94	221
Changes Recognized in Comprehensive Income
Net actuarial (gain) loss during period	(248)	284	(430)
Amortization of actuarial loss	(15)	5	(19)
Prior service (credits) costs during period	3	0	(345)
Amortization of prior service (costs) credits	28	28	(14)
Total changes recognized in other comprehensive income	(232)	317	(808)
Recognized in Net Periodic Benefit Cost and Other Comprehensive Income	(109)	411	(587)
U.S. \| Pension Benefits
Net Periodic Benefit Cost
Service cost	480	489	494
Interest cost	370	366	377
Expected return on plan assets	(636)	(597)	(723)
Amortization of prior service costs (credits)	2	(5)	(9)
Recognized actuarial losses	304	340	335
Settlement losses	411	436	511
Curtailment losses (gains)	0	0	0
Total net periodic benefit cost	931	1,029	985
Changes Recognized in Comprehensive Income
Net actuarial (gain) loss during period	151	381	690
Amortization of actuarial loss	(715)	(776)	(846)
Prior service (credits) costs during period	0	0	0
Amortization of prior service (costs) credits	(2)	5	9
Total changes recognized in other comprehensive income	(566)	(390)	(147)
Recognized in Net Periodic Benefit Cost and Other Comprehensive Income	365	639	838
Int’l. \| Pension Benefits
Net Periodic Benefit Cost
Service cost	141	151	159
Interest cost	206	219	261
Expected return on plan assets	(253)	(239)	(243)
Amortization of prior service costs (credits)	10	13	14
Recognized actuarial losses	29	44	47
Settlement losses	33	2	6
Curtailment losses (gains)	3	0	0
Total net periodic benefit cost	169	190	244
Changes Recognized in Comprehensive Income
Net actuarial (gain) loss during period	12	(94)	55
Amortization of actuarial loss	(62)	(46)	(53)
Prior service (credits) costs during period	23	1	0
Amortization of prior service (costs) credits	(13)	(13)	(14)
Total changes recognized in other comprehensive income	(40)	(152)	(12)
Recognized in Net Periodic Benefit Cost and Other Comprehensive Income	$ 129	$ 38	$ 232

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

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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.

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Amount, before tax, of cost (credit) of benefit change attributable to participants' prior service from plan amendment or plan initiation of defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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