Quarterly Supplementary Data (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 1,263	$ 1,278	$ 1,316	$ 1,285	$ 1,262	$ 1,280	$ 1,214	$ 1,189	$ 5,142	$ 4,945	$ 4,531
Income before income taxes	216	243	248	174	236	259	107	119	881	721	714
Net Income (Loss) Attributable to Parent	$ 156	$ 174	$ 176	$ 128	$ 167	$ 183	$ 84	$ 91	$ 634	$ 525	$ 517
Basic (in usd per share)	$ 0.95	$ 1.06	$ 1.07	$ 0.78	$ 1.03	$ 1.12	$ 0.51	$ 0.56	$ 3.87	$ 3.21	$ 3.16
Diluted (in usd per share)	$ 0.94	$ 1.05	$ 1.06	$ 0.77	$ 1.02	$ 1.11	$ 0.51	$ 0.55	$ 3.83	$ 3.18	$ 3.12