Employee Benefit Plans - Level 3 Rollforward (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Domestic Pension Plans [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance		$ 2,718		$ 2,711
Ending balance		2,489		2,718		$ 2,711
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]	110
Ending balance	[1]	112		110
Domestic Pension Plans [Member] | Limited Partnership Interests [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	[2]	70
Ending balance	[2]	65		70
Domestic Pension Plans [Member] | Limited Partnership Interests [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance		70	[1],[2]	86		96
Defined Benefit Plan, Actual Return on Plan Assets Still Held		5		(1)		16
Defined Benefit Plan, Purchases, Sales, and Settlements		(10)		(15)		(26)
Ending balance		65	[1],[2]	70	[1],[2]	86
Domestic Pension Plans [Member] | Real Estate Funds [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance		40
Ending balance		47		40
Domestic 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		40	[1]	31		26
Defined Benefit Plan, Actual Return on Plan Assets Still Held		7		4		5
Defined Benefit Plan, Purchases, Sales, and Settlements		0		5		0
Ending balance		47	[1]	40	[1]	31
Domestic Other Postretirement Plans [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance		858		852
Ending balance		662		858		852
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	[3]	5
Ending balance	[3]	4		5
Domestic Other Postretirement Plans [Member] | Limited Partnership Interests [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	[4]	5
Ending balance	[4]	4		5
Domestic Other Postretirement Plans [Member] | Limited Partnership Interests [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance		5	[3],[4]	6		7
Defined Benefit Plan, Actual Return on Plan Assets Still Held		0		0		1
Defined Benefit Plan, Purchases, Sales, and Settlements		(1)		(1)		(2)
Ending balance		4	[3],[4]	5	[3],[4]	6
UK Pension Plans [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance		2,368		2,177
Foreign Currency Exchange Rate Changes		(128)		(145)
Ending balance		2,276		2,368		2,177
UK Pension Plans [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	[5]	199
Ending balance	[5]	204		199
UK Pension Plans [Member] | Real Estate Funds [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance		199
Ending balance		204		199
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		199	[5]	179		163
Defined Benefit Plan, Actual Return on Plan Assets Still Held		18		33		12
Foreign Currency Exchange Rate Changes		(13)		(13)		4
Ending balance		$ 204	[5]	$ 199	[5]	$ 179

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

[2] Limited partnership interests include several funds that invest primarily in real estate, buyout, growth equity and venture capital.

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

[4] Limited partnership interests include several funds that invest primarily in real estate, buyout, growth equity and venture capital.

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