Employee Benefit Plans - Fair values of pension plan assets (Details) - USD ($) $ in Millions	Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Fair values of our pension plan assets
Fair value of participating interest in annuity contract	$ 125		$ 116
Net payables receivables related to security transactions	32		21
Fair Value, Inputs, Level 3 [Member]
Fair values of our pension plan assets
Fair value of participating interest in annuity contract	125		116
United States Pension Plans of US Entity, Defined Benefit [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	2,606		3,266		$ 3,092
United States Pension Plans of US Entity, Defined Benefit [Member] | U.S. (Equity Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	782		1,049
United States Pension Plans of US Entity, Defined Benefit [Member] | International (Equity Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	485		671
United States Pension Plans of US Entity, Defined Benefit [Member] | Common/Collective Trusts(Equity Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	569		542
United States Pension Plans of US Entity, Defined Benefit [Member] | Government (Debt Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	141		207
United States Pension Plans of US Entity, Defined Benefit [Member] | Corporate (Debt Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	348		430
United States Pension Plans of US Entity, Defined Benefit [Member] | Agency and Mortgage Backed Securities(Debt Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	80		115
United States Pension Plans of US Entity, Defined Benefit [Member] | Cash and Cash Equivalents [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	60		67
United States Pension Plans of US Entity, Defined Benefit [Member] | Private Equity Funds [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	0		0
United States Pension Plans of US Entity, Defined Benefit [Member] | Derivatives [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	(7)		2
United States Pension Plans of US Entity, Defined Benefit [Member] | Real Estate [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	63		55
United States Pension Plans of US Entity, Defined Benefit [Member] | Excluding reconciling items [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	2,521	[1]	3,138	[2]
United States Pension Plans of US Entity, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. (Equity Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	777		1,039
United States Pension Plans of US Entity, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | International (Equity Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	485		671
United States Pension Plans of US Entity, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Government (Debt Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	85		132
United States Pension Plans of US Entity, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Derivatives [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	0		5
United States Pension Plans of US Entity, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Excluding reconciling items [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	1,347	[1]	1,847	[2]
United States Pension Plans of US Entity, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. (Equity Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	3		2
United States Pension Plans of US Entity, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Common/Collective Trusts(Equity Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	569		542
United States Pension Plans of US Entity, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Government (Debt Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	56		75
United States Pension Plans of US Entity, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate (Debt Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	331		426
United States Pension Plans of US Entity, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Agency and Mortgage Backed Securities(Debt Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	80		115
United States Pension Plans of US Entity, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Cash and Cash Equivalents [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	60		67
United States Pension Plans of US Entity, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Derivatives [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	(7)		(3)
United States Pension Plans of US Entity, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Excluding reconciling items [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	1,092	[1]	1,224	[2]
United States Pension Plans of US Entity, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. (Equity Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	2		8
United States Pension Plans of US Entity, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Corporate (Debt Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	17		4
United States Pension Plans of US Entity, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Private Equity Funds [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets			0
United States Pension Plans of US Entity, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Real Estate [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	63		55
United States Pension Plans of US Entity, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Excluding reconciling items [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	82	[1]	67	[2]
Foreign Pension Plans, Defined Benefit [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	3,063		3,278		$ 3,132
Foreign Pension Plans, Defined Benefit [Member] | U.S. (Equity Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	609		628
Foreign Pension Plans, Defined Benefit [Member] | International (Equity Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	450		445
Foreign Pension Plans, Defined Benefit [Member] | Common/Collective Trusts(Equity Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	214		227
Foreign Pension Plans, Defined Benefit [Member] | Mutual Funds (Equity Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	340		338
Foreign Pension Plans, Defined Benefit [Member] | Government (Debt Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	493		624
Foreign Pension Plans, Defined Benefit [Member] | Corporate (Debt Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	172		166
Foreign Pension Plans, Defined Benefit [Member] | Agency and Mortgage Backed Securities(Debt Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	36		47
Foreign Pension Plans, Defined Benefit [Member] | Common/Collective Trusts (Debt Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	406		396
Foreign Pension Plans, Defined Benefit [Member] | Mutual Funds (Debt Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	136		167
Foreign Pension Plans, Defined Benefit [Member] | Cash and Cash Equivalents [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	56		68
Foreign Pension Plans, Defined Benefit [Member] | Private Equity Funds [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	0		1
Foreign Pension Plans, Defined Benefit [Member] | Derivatives [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	(26)		(4)
Foreign Pension Plans, Defined Benefit [Member] | Real Estate [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	169		166
Foreign Pension Plans, Defined Benefit [Member] | Excluding reconciling items [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	3,055	[1]	3,269	[2]
Foreign Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. (Equity Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	609		628
Foreign Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | International (Equity Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	450		445
Foreign Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Mutual Funds (Equity Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	234		241
Foreign Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Government (Debt Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	493		624
Foreign Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Mutual Funds (Debt Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	136		167
Foreign Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Cash and Cash Equivalents [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	46		50
Foreign Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Derivatives [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	(26)		(4)
Foreign Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Excluding reconciling items [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	1,942	[1]	2,151	[2]
Foreign Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Common/Collective Trusts(Equity Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	214		227
Foreign Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Mutual Funds (Equity Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	106		97
Foreign Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate (Debt Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	172		166
Foreign Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Agency and Mortgage Backed Securities(Debt Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	36		46
Foreign Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Common/Collective Trusts (Debt Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	406		396
Foreign Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Cash and Cash Equivalents [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	10		18
Foreign Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Derivatives [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets			0
Foreign Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Excluding reconciling items [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	944	[1]	950	[2]
Foreign Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Agency and Mortgage Backed Securities(Debt Securities) [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	0		1
Foreign Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Private Equity Funds [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	0		1
Foreign Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Real Estate [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	169		166
Foreign Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Excluding reconciling items [Member]
Fair values of our pension plan assets
Fair Value of Option Plan Assets	$ 169	[1]	$ 168	[2]

[1] Excludes the participating interest in the annuity contract with a net asset value of $125 million and net receivables related to security transactions of $32 million.

[2] Excludes the participating interest in the annuity contract with a net asset value of $116 million and net receivables related to security transactions of $21 million.