Derivative Financial Instruments (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Derivative Financial Instruments
Amount of gain (loss) recognized in OCI on derivative	$ (22)	[1]	$ 1	[1]	$ 4	[1]
Amount of (gain) loss reclassified from OCI into revenue	5	[1]	(2)	[1]	(2)	[1]
Amount of (gain) loss reclassified from OCI into cost of revenue	$ 1	[1]	$ 2	[1]	$ (1)	[1]

[1] Effective portion