Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 1,095	$ 897	$ 932	$ 847	$ 994	$ 902	$ 920	$ 837	$ 3,771	$ 3,653	$ 3,916
Gross Profit	406	357	369	329	390	351	348	315	1,461	1,404	1,513
Operating income	109	109	109	79	142	120	104	83	406	449	463
Net income	$ 50	$ 73	$ 71	$ 66	$ 114	$ 88	$ 74	$ 64	$ 260	$ 340	$ 337
Basic (in dollars per share)	$ 0.28	$ 0.41	$ 0.39	$ 0.37	$ 0.64	$ 0.48	$ 0.41	$ 0.35	$ 1.45	$ 1.88	$ 1.84
Diluted (in dollars per share)	$ 0.28	$ 0.41	$ 0.39	$ 0.37	$ 0.63	$ 0.48	$ 0.41	$ 0.35	$ 1.45	$ 1.87	$ 1.83