Employee Benefit Plans - Defined Benefit Plans Measured Using Significant Unobservable Inputs Level 3 (Details) - Pension Plan - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value of plan assets -beginning	$ 8,087
Fair value of plan assets - ending	8,878	$ 8,087
U.S.
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value of plan assets -beginning	2,358	3,224
Fair value of plan assets - ending	2,493	2,358
U.S. | Real estate
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value of plan assets -beginning	28
Fair value of plan assets - ending	15	28
U.S. | Guaranteed insurance contracts
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value of plan assets -beginning	0
Fair value of plan assets - ending	0	0
U.S. | Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value of plan assets -beginning	0
Fair value of plan assets - ending	5	0
U.S. | Level 3 | Real estate
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value of plan assets -beginning	0	0
Purchases	5	0
Sales	0	0
Realized losses		(4)
Unrealized gains	0	4
Currency translation	0	0
Fair value of plan assets - ending	5	0
U.S. | Level 3 | Guaranteed insurance contracts
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value of plan assets -beginning	0
Fair value of plan assets - ending	0	0
Foreign Plan
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value of plan assets -beginning	5,729	6,308
Fair value of plan assets - ending	6,385	5,729
Foreign Plan | Real estate
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value of plan assets -beginning	367
Fair value of plan assets - ending	335	367
Foreign Plan | Guaranteed insurance contracts
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value of plan assets -beginning	92
Fair value of plan assets - ending	90	92
Foreign Plan | Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value of plan assets -beginning	308	244
Purchases	2	23
Sales	(9)	(7)
Realized losses		0
Unrealized gains	15	58
Currency translation	(2)	(10)
Fair value of plan assets - ending	314	308
Foreign Plan | Level 3 | Real estate
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value of plan assets -beginning	210	137
Purchases	0	22
Sales	0	(1)
Realized losses		0
Unrealized gains	9	62
Currency translation	0	(10)
Fair value of plan assets - ending	219	210
Foreign Plan | Level 3 | Private equity funds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value of plan assets -beginning	6	7
Purchases	0	0
Sales	(5)	0
Realized losses		0
Unrealized gains	4	(4)
Currency translation	0	3
Fair value of plan assets - ending	5	6
Foreign Plan | Level 3 | Guaranteed insurance contracts
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value of plan assets -beginning	92	100
Purchases	2	1
Sales	(4)	(6)
Realized losses		0
Unrealized gains	2	0
Currency translation	(2)	(3)
Fair value of plan assets - ending	$ 90	$ 92