Earnings Per Share (Calculation of EPS) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ 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
Basic and diluted net earnings per share:
Net income (in usd)	$ 50	$ 73	$ 71	$ 66	$ 114	$ 88	$ 74	$ 64	$ 260	$ 340	$ 337
Shares
Weighted average common shares outstanding									179,069	180,854	183,030
Add: Participating securities									37	39	47
Weighted average common shares outstanding — Basic									179,106	180,893	183,077
Plus incremental shares from assumed conversions:
Weighted average common shares outstanding — Diluted									180,038	181,737	184,249
Basic earnings per share (in usd 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 earnings per share (in usd per share)	$ 0.28	$ 0.41	$ 0.39	$ 0.37	$ 0.63	$ 0.48	$ 0.41	$ 0.35	$ 1.45	$ 1.87	$ 1.83
Stock Options
Plus incremental shares from assumed conversions:
Dilutive effect of common shares									499	465	643
Restricted Stock
Plus incremental shares from assumed conversions:
Dilutive effect of common shares									433	379	529