Derivatives and Hedging - Offsetting of financial assets and derivatives assets (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Derivative [Line Items]
Gross Amounts of Recognized Assets	$ 46		$ 80
Gross Amounts Offset in the Statement of Financial Position	(14)		(30)
Net Amounts of Assets Presented in the Statement of Financial Position	32	[1]	50	[1]
Other Current Assets [Member]
Derivative [Line Items]
Gross Amounts of Recognized Assets	24		46
Net Amounts of Assets Presented in the Statement of Financial Position	12		18
Other Noncurrent Assets [Member]
Derivative [Line Items]
Gross Amounts of Recognized Assets	22		34
Net Amounts of Assets Presented in the Statement of Financial Position	20		32
Designated as Hedging Instrument [Member]
Derivative [Line Items]
Gross Amounts of Recognized Assets	46	[2]	80	[2]
Gross Amounts Offset in the Statement of Financial Position	(14)		(30)
Net Amounts of Assets Presented in the Statement of Financial Position	32	[1]	50	[1]
Designated as Hedging Instrument [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Gross Amounts of Recognized Assets	0	[2]	9	[2]
Gross Amounts Offset in the Statement of Financial Position	0		0
Net Amounts of Assets Presented in the Statement of Financial Position	0	[1]	9	[1]
Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Gross Amounts of Recognized Assets	46	[2]	71	[2]
Gross Amounts Offset in the Statement of Financial Position	(14)		(30)
Net Amounts of Assets Presented in the Statement of Financial Position	32	[1]	41	[1]
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Gross Amounts of Recognized Assets	46	[2]	80	[2]
Not Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Gross Amounts of Recognized Assets	0	[2],[3]	0	[2],[3]
Gross Amounts Offset in the Statement of Financial Position	0		0
Net Amounts of Assets Presented in the Statement of Financial Position	$ 0	[1]	$ 0	[1]

[1] Included within Other current assets ($12 million in 2014 and $18 million in 2013, respectively) or Other non-current assets ($20 million in 2014 and $32 million in 2013, respectively)

[2] Included within Other current assets ($24 million in 2014 and $46 million in 2013, respectively) or Other non-current assets ($22 million in 2014 and $34 million in 2013, respectively)

[3] 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.