Earnings Per Share (Calculation of EPS) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Basic and diluted net earnings per share:
Net income (in usd)	$ 118	$ 65	$ 139	$ 79	$ 225	$ 130	$ 115	$ 79	$ 401	$ 549	$ 331
Net income									$ 401	$ 549	$ 330
Shares
Weighted average common shares outstanding									179,958	179,750	179,602
Add: Participating securities									29	27	27
Weighted average common shares outstanding — Basic									179,987	179,777	179,629
Plus incremental shares from assumed conversions:
Weighted average common shares outstanding — Diluted									181,196	181,132	180,857
Basic earnings per share (in usd per share)	$ 0.66	$ 0.36	$ 0.77	$ 0.44	$ 1.25	$ 0.73	$ 0.64	$ 0.44	$ 2.23	$ 3.05	$ 1.84
Diluted earnings per share (in usd per share)	$ 0.65	$ 0.36	$ 0.77	$ 0.43	$ 1.24	$ 0.72	$ 0.64	$ 0.43	$ 2.21	$ 3.03	$ 1.83
Stock Options
Plus incremental shares from assumed conversions:
Dilutive effect of common shares									803	876	712
Restricted Stock
Plus incremental shares from assumed conversions:
Dilutive effect of common shares									406	479	516