Employee Benefit Plans - Accumulated Benefit Obligation in Excess of Plan Assets (Details) - Pension Plan [Member] - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation		$ 4,415	$ 5,490
Accumulated Benefit Obligation		4,393	5,463
Fair value of plan assets		2,982	3,947
Fair Value of Pension Plan Assets		8,087	9,532
Pension Benefit Obligation		9,241
Net Funded Status		(1,154)
U.S.
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation		3,234	4,180
Accumulated Benefit Obligation		3,234	4,179
Fair value of plan assets		2,358	3,224
Fair Value of Pension Plan Assets		2,358	3,224	$ 2,774
Pension Benefit Obligation		3,234	4,180	4,161
Net Funded Status	[1]	(876)	(956)
U.K.
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Pension Plan Assets		3,730
Pension Benefit Obligation		3,501
Net Funded Status		229
Netherlands
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Pension Plan Assets		968
Pension Benefit Obligation		1,040
Net Funded Status		(72)
Canada
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Pension Plan Assets		653
Pension Benefit Obligation		656
Net Funded Status		(3)
Germany
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Pension Plan Assets		0
Pension Benefit Obligation		355
Net Funded Status		(355)
Foreign Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation		1,181	1,310
Accumulated Benefit Obligation		1,159	1,284
Fair value of plan assets		624	723
Fair Value of Pension Plan Assets		5,729	6,308	5,384
Pension Benefit Obligation		6,007	6,703	$ 6,160
Net Funded Status	[1]	(278)	(395)
Other
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Pension Plan Assets		378
Pension Benefit Obligation		455
Net Funded Status		(77)
Underfunded Plan [Member] | U.S.
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation		2,918	3,830
Accumulated Benefit Obligation		2,918	3,829
Fair value of plan assets		2,358	3,224
Underfunded Plan [Member] | Foreign Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation		725	814
Accumulated Benefit Obligation		713	799
Fair value of plan assets		624	723
Unfunded Plan [Member] | U.S.
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation		316	350
Accumulated Benefit Obligation		316	350
Fair value of plan assets		0	0
Fair Value of Pension Plan Assets		0
Pension Benefit Obligation		316
Net Funded Status		(316)
Unfunded Plan [Member] | Foreign Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation		456	496
Accumulated Benefit Obligation		446	485
Fair value of plan assets		0	$ 0
Funded Plan [Member] | U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Pension Plan Assets		2,358
Pension Benefit Obligation		2,918
Net Funded Status		$ (560)

[1] Includes under-funded and unfunded plans.