Net Income Per Common Share (Basic And Diluted Net Income Per Share) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Net income	$ 211	$ 292	$ 259	$ 929
Income allocated to participating securities	0	2	1	5
Preferred stock dividends	8	0	8	0
Net income attributable to common shares	$ 203	$ 290	$ 250	$ 924
Basic average shares	139.0	147.0	139.0	152.0
Basic net income per common share	$ 1.45	$ 1.98	$ 1.79	$ 6.08
Basic average shares	139.0	147.0	139.0	152.0
Net effect of the assumed exercise of stock options	1.0	1.0	1.0	2.0
Diluted average shares	140.0	148.0	140.0	154.0
Diluted net income per common share	$ 1.44	$ 1.96	$ 1.78	$ 6.02