Quarterly Financial Data (Unaudited) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 1,042	$ 963	$ 1,005	$ 906	$ 1,033	$ 965	$ 960	$ 879	$ 3,916	$ 3,837	$ 3,791
Gross Profit	407	376	388	342	410	384	371	334	1,513	1,499	1,502
Operating income	141	130	116	76	129	98	70	66	463	363	443
Net income	$ 96	$ 106	$ 86	$ 49	$ 68	$ 73	$ 46	$ 41	$ 337	$ 228	$ 297
Basic (in dollars per share)	$ 0.53	$ 0.58	$ 0.47	$ 0.27	$ 0.37	$ 0.39	$ 0.25	$ 0.22	$ 1.84	$ 1.23	$ 1.60
Diluted (in dollars per share)	$ 0.52	$ 0.58	$ 0.47	$ 0.27	$ 0.37	$ 0.39	$ 0.25	$ 0.22	$ 1.83	$ 1.22	$ 1.59