Employee Benefit Plans - Level 3 Rollforward (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Domestic Pension Plans [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance		$ 2,489		$ 2,718
Ending balance		2,525		2,489		$ 2,718
Domestic Pension Plans [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	[1]	0
Ending balance	[1]	0		0
Domestic Other Postretirement Plans [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance		662		858
Ending balance		666		662		858
Domestic Other Postretirement Plans [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	[2]	0
Ending balance	[2]	0		0
UK Pension Plans [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance		2,276		2,368
Foreign Currency Exchange Rate Changes		(397)		(128)
Ending balance		2,169		2,276		2,368
UK Pension Plans [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	[3]	204
Ending balance	[3]	105		204
UK Pension Plans [Member] | Real Estate Funds [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance		204
Ending balance		105		204
UK Pension Plans [Member] | Real Estate Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance		204	[3]	199		179
Defined Benefit Plan, Actual Return on Plan Assets Still Held		10		18		33
Defined Benefit Plan, Purchases, Sales, and Settlements		(80)		0		0
Foreign Currency Exchange Rate Changes		(29)		(13)		(13)
Ending balance		$ 105	[3]	$ 204	[3]	$ 199

[1] Refer to Note 15 for additional discussion regarding the three levels of the fair value hierarchy.

[2] Refer to Note 15 for additional discussion regarding the three levels of the fair value hierarchy.

[3] Refer to Note 15 for additional discussion regarding the three levels of the fair value hierarchy.