Employee Benefit Plans - Accumulated Benefit Obligation in Excess of Plan Assets (Details) - Pension Plan [Member] - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation		$ 5,490	$ 9,141
Accumulated Benefit Obligation		5,463	8,965
Fair value of plan assets		3,947	6,968
Defined Benefit Plan, Fair Value of Plan Assets		9,532	8,158
Pension Benefit Obligation		10,883
Net Funded Status		(1,351)
Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation		4,180	4,161
Accumulated Benefit Obligation		4,179	4,161
Fair value of plan assets		3,224	2,774
Defined Benefit Plan, Fair Value of Plan Assets		3,224	2,774	$ 2,806
Pension Benefit Obligation		4,180	4,161	4,126
Net Funded Status	[1]	(956)	(1,387)
Foreign Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation		1,310	4,980
Accumulated Benefit Obligation		1,284	4,804
Fair value of plan assets		723	4,194
Defined Benefit Plan, Fair Value of Plan Assets		6,308	5,384	5,353
Pension Benefit Obligation		6,703	6,160	$ 6,308
Net Funded Status	[1]	(395)	(776)
Foreign Plan [Member] | UNITED KINGDOM
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		4,098
Pension Benefit Obligation		3,948
Net Funded Status		150
Foreign Plan [Member] | Canada
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		749
Pension Benefit Obligation		777
Net Funded Status		(28)
Foreign Plan [Member] | Pension Plans All Other Countries [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		1,461
Pension Benefit Obligation		1,978
Net Funded Status		(517)
Underfunded Plan [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation		3,830	3,820
Accumulated Benefit Obligation		3,829	3,820
Fair value of plan assets		3,224	2,774
Underfunded Plan [Member] | Foreign Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation		814	4,535
Accumulated Benefit Obligation		799	4,368
Fair value of plan assets		723	4,194
Unfunded Plan [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation		350	341
Accumulated Benefit Obligation		350	341
Fair value of plan assets		0	0
Defined Benefit Plan, Fair Value of Plan Assets		0
Pension Benefit Obligation		350
Net Funded Status		(350)
Unfunded Plan [Member] | Foreign Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation		496	445
Accumulated Benefit Obligation		485	436
Fair value of plan assets		0	$ 0
Funded Plan [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		3,224
Pension Benefit Obligation		3,830
Net Funded Status		$ (606)

[1] Includes under-funded and unfunded plans.