Employee Benefit Plans - Funded Status (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016	Dec. 31, 2015
Domestic Pension Plans [Member]
Defined Benefit Plan, Funded Status of Plan [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	$ 2,489	$ 2,718	$ 2,718	$ 2,525	$ 2,489
Defined Benefit Plan, Benefit Obligation	2,934	3,119	3,119	2,952	2,934
Defined Benefit Plan, Funded Status of Plan				(427)	(445)
Other assets				26	7
Other current liabilities				(15)	(15)
Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent				(438)	(437)
Defined Benefit Plan, Amounts Recognized in Balance Sheet				(427)	(445)
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	2,489	2,718
Defined Benefit Plan, Contributions by Employer	78	13
Defined Benefit Plan, Contributions by Plan Participants	0	0
Defined Benefit Plan, Actual Return on Plan Assets	163	(17)
Defined Benefit Plan, Settlements, Plan Assets	(11)	23
Defined Benefit Plan, Benefits Paid	(194)	(202)
Ending balance	2,525	2,489	2,718
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Beginning balance	2,934	3,119
Defined Benefit Plan, Service Cost	29	33	36
Defined Benefit Plan, Interest Cost	126	121	131
Defined Benefit Plan, Contributions by Plan Participants	0	0
Defined Benefit Plan, Actuarial Gain (Loss)	67	(110)
Defined Benefit Plan, Plan Amendments	1	(4)
Defined Benefit Plan, Settlements, Benefit Obligation	(11)	(23)
Benefits Paid	(194)	(202)
Ending balance	2,952	2,934	3,119
Defined Benefit Plan, Accumulated Benefit Obligation				2,929	2,906
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets [Abstract]
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets, Aggregate Fair Value of Plan Assets				1,841	1,811
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets, Aggregate Benefit Obligation				2,294	2,263
Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets, Aggregate Accumulated Benefit Obligation				2,278	2,244
Domestic Other Postretirement Plans [Member]
Defined Benefit Plan, Funded Status of Plan [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	662	858	858	666	662
Defined Benefit Plan, Benefit Obligation	740	936	936	734	740
Defined Benefit Plan, Funded Status of Plan				(68)	(78)
Other assets				19	15
Other current liabilities				0	0
Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent				(87)	(93)
Defined Benefit Plan, Amounts Recognized in Balance Sheet				(68)	(78)
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	662	858
Defined Benefit Plan, Contributions by Employer	2	2
Defined Benefit Plan, Contributions by Plan Participants	10	9
Defined Benefit Plan, Actual Return on Plan Assets	41	0
Defined Benefit Plan, Settlements, Plan Assets	0	150
Defined Benefit Plan, Benefits Paid	(49)	(57)
Ending balance	666	662	858
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Beginning balance	740	936
Defined Benefit Plan, Service Cost	9	11	14
Defined Benefit Plan, Interest Cost	31	31	46
Defined Benefit Plan, Contributions by Plan Participants	10	9
Defined Benefit Plan, Actuarial Gain (Loss)	(7)	(43)
Defined Benefit Plan, Plan Amendments	0	3
Defined Benefit Plan, Settlements, Benefit Obligation	0	(150)
Benefits Paid	(49)	(57)
Ending balance	734	740	936
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets [Abstract]
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets, Aggregate Fair Value of Plan Assets				413	413
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets, Aggregate Benefit Obligation				500	505
UK Pension Plans [Member]
Defined Benefit Plan, Funded Status of Plan [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	2,276	2,368	2,368	2,169	2,276
Defined Benefit Plan, Benefit Obligation	2,142	2,279	2,279	2,125	2,142
Defined Benefit Plan, Funded Status of Plan				44	134
Other assets				44	134
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	2,276	2,368
Defined Benefit Plan, Contributions by Employer	55	77
Defined Benefit Plan, Contributions by Plan Participants	1	2
Defined Benefit Plan, Actual Return on Plan Assets	349	48
Defined Benefit Plan, Benefits Paid	(115)	(91)
Foreign Currency Exchange Rate Changes	(397)	(128)
Ending balance	2,169	2,276	2,368
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Beginning balance	2,142	2,279
Defined Benefit Plan, Service Cost	20	24	24
Defined Benefit Plan, Interest Cost	72	79	95
Defined Benefit Plan, Contributions by Plan Participants	1	2
Defined Benefit Plan, Actuarial Gain (Loss)	387	(30)
Benefits Paid	(115)	(91)
Foreign currency exchange rate changes	(382)	(121)
Ending balance	$ 2,125	$ 2,142	$ 2,279
Defined Benefit Plan, Accumulated Benefit Obligation				1,858	1,891
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plans, Supplemental Employee Retirement Plans [Abstract]
Life Insurance, Corporate or Bank Owned, Amount				$ 242	$ 228