Derivatives and Hedging - Notional and fair values of derivative instruments (Details) - USD ($) $ in Millions		9 Months Ended
		Sep. 30, 2015	Dec. 31, 2014
Derivatives, Fair Value
Notional Amount		$ 1,141	$ 1,365
Derivative Assets	[1]	34	46
Derivative Liabilities	[2]	$ 51	58
Term of derivative contract		30 days
Gross Amounts Offset in the Statement of Financial Position		$ (14)	(14)
Net Amounts of Assets Presented in the Statement of Financial Position	[3]	20	32
Gross Amounts Offset in the Statement of Financial Position		(15)	(14)
Net Amounts of Liabilities Presented in the Statement of Financial Position	[4]	36	44
Other Current Assets [Member]
Derivatives, Fair Value
Derivative Assets		16	24
Net Amounts of Assets Presented in the Statement of Financial Position		8	12
Other Noncurrent Assets [Member]
Derivatives, Fair Value
Derivative Assets		18	22
Net Amounts of Assets Presented in the Statement of Financial Position		12	20
Other Current Liabilities [Member]
Derivatives, Fair Value
Derivative Liabilities		40	52
Net Amounts of Liabilities Presented in the Statement of Financial Position		32	40
Other Noncurrent Liabilities [Member]
Derivatives, Fair Value
Derivative Liabilities		11	6
Net Amounts of Liabilities Presented in the Statement of Financial Position		4	4
Derivatives accounted for as hedges [Member]
Derivatives, Fair Value
Notional Amount		965	1,200
Derivative Assets	[1]	34	46
Derivative Liabilities	[2]	50	58
Gross Amounts Offset in the Statement of Financial Position		(14)	(14)
Net Amounts of Assets Presented in the Statement of Financial Position	[3]	20	32
Gross Amounts Offset in the Statement of Financial Position		(15)	(14)
Net Amounts of Liabilities Presented in the Statement of Financial Position	[4]	35	44
Derivatives accounted for as hedges [Member] | Interest rate contracts [Member]
Derivatives, Fair Value
Notional Amount		0	0
Derivative Assets	[1]	0	0
Derivative Liabilities	[2]	0	0
Gross Amounts Offset in the Statement of Financial Position		0	0
Net Amounts of Assets Presented in the Statement of Financial Position	[3]	0	0
Gross Amounts Offset in the Statement of Financial Position		0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	[4]	0	0
Derivatives accounted for as hedges [Member] | Foreign exchange contracts [Member]
Derivatives, Fair Value
Notional Amount		965	1,200
Derivative Assets	[1]	34	46
Derivative Liabilities	[2]	50	58
Gross Amounts Offset in the Statement of Financial Position		(14)	(14)
Net Amounts of Assets Presented in the Statement of Financial Position	[3]	20	32
Gross Amounts Offset in the Statement of Financial Position		(15)	(14)
Net Amounts of Liabilities Presented in the Statement of Financial Position	[4]	35	44
Not Designated as Hedging Instrument [Member] | Foreign exchange contracts [Member]
Derivatives, Fair Value
Notional Amount	[5]	176	165
Derivative Assets	[1],[5]	0	0
Derivative Liabilities	[2],[5]	1	0
Gross Amounts Offset in the Statement of Financial Position		0	0
Net Amounts of Assets Presented in the Statement of Financial Position	[3]	0	0
Gross Amounts Offset in the Statement of Financial Position		0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	[4]	$ 1	$ 0

[1] Included within Other current assets ($16 million at September 30, 2015 and $24 million at December 31, 2014) or Other non-current assets ($18 million at September 30, 2015 and $22 million at December 31, 2014).

[2] Included within Other current liabilities ($40 million at September 30, 2015 and $52 million at December 31, 2014) or Other non-current liabilities ($11 million at September 30, 2015 and $6 million at December 31, 2014).

[3] Included within Other current assets ($8 million at September 30, 2015 and $12 million at December 31, 2014) or Other non-current assets ($12 million at September 30, 2015 and $20 million at December 31, 2014).

[4] Included within Other current liabilities ($32 million at September 30, 2015 and $40 million at December 31, 2014) or Other non-current liabilities ($4 million at September 30, 2015 and $4 million at December 31, 2014).

[5] These contracts typically are for 30 day durations and executed close to the last day of the most recent reporting month, thereby resulting in nominal fair values at the balance sheet date.