Derivatives and Hedging - Notional and fair values of derivative instruments (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Derivative [Line Items]
Derivative Assets	$ 46		$ 80
Derivative Liabilities	58		93
Other Current Assets [Member]
Derivative [Line Items]
Derivative Assets	24		46
Other Noncurrent Assets [Member]
Derivative [Line Items]
Derivative Assets	22		34
Other Current Liabilities [Member]
Derivative [Line Items]
Derivative Liabilities	52		51
Other Noncurrent Liabilities [Member]
Derivative [Line Items]
Derivative Liabilities	6		42
Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount	1,200		1,362
Derivative Assets	46	[1]	80	[1]
Derivative Liabilities	58	[2]	93	[2]
Designated as Hedging Instrument [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Notional Amount	0		171
Derivative Assets	0	[1]	9	[1]
Derivative Liabilities	0	[2]	0	[2]
Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Notional Amount	1,200		1,191
Derivative Assets	46	[1]	71	[1]
Derivative Liabilities	58	[2]	93	[2]
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount	1,365		1,577
Derivative Assets	46	[1]	80	[1]
Derivative Liabilities	58	[2]	93	[2]
Not Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Notional Amount	165	[3]	215	[3]
Derivative Assets	0	[1],[3]	0	[1],[3]
Derivative Liabilities	$ 0	[2],[3]	$ 0	[2],[3]
Term of contract	30 days

[1] 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)

[2] Included within Other current liabilities ($52 million in 2014 and $51 million in 2013, respectively) or Other non-current liabilities ($6 million in 2014 and $42 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.