Employee Benefit Plans - Change in Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Foreign Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	$ 1,086	$ 978	$ 1,009
Net service cost	8	7	12
Interest cost	20	28	42
Expected return on plan assets	(35)	(36)	(60)
Amortization of prior service cost	1	1	1
Curtailment	0	0	2
Settlement	0	0	(427)
Actuarial loss	0	69	2
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	(6)	69	422
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss)	80	136
Company contributions	25	31
Defined Benefit Plan, Benefit Obligation, Benefits Paid	(75)	(75)
Defined Benefit Plan, Plan Assets, Foreign Currency Translation Gain (Loss)	77	(124)
Plan participant contributions	1	1
U.S. Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	1,444	1,722	1,726
Net service cost	0	0	0
Interest cost	71	90	87
Expected return on plan assets	(57)	(72)	(72)
Amortization of prior service cost	0	0	0
Curtailment	0	0	0
Settlement	0	0	0
Actuarial loss	28	16	27
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	42	34	42
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss)	149	109
Company contributions	0	0
Defined Benefit Plan, Benefit Obligation, Benefits Paid	(427)	(113)
Defined Benefit Plan, Plan Assets, Foreign Currency Translation Gain (Loss)	0	0
Plan participant contributions	0	0
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	2,530	2,700	2,735
Net service cost	8	7	12
Interest cost	91	118	129
Expected return on plan assets	(92)	(108)	(132)
Amortization of prior service cost	1	1	1
Curtailment	0	0	2
Settlement	0	0	(427)
Actuarial loss	28	85	29
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	36	103	$ 464
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss)	229	245
Company contributions	25	31
Defined Benefit Plan, Benefit Obligation, Benefits Paid	(502)	(188)
Defined Benefit Plan, Plan Assets, Foreign Currency Translation Gain (Loss)	77	(124)
Plan participant contributions	$ 1	$ 1