Net Income Per Common Share (Basic And Diluted Net Income Per Common Share) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Net income	$ 339	$ 281
Income allocated to participating securities	2	2
Net income attributable to common shares	$ 337	$ 279
Basic average common shares	158	172
Basic net income per common share	$ 2.14	$ 1.62
Basic average common shares	158	172
Net effect of the assumed exercise of stock options	2	2
Net effect of the assumed exercise of warrants	0	1
Diluted average common shares	160	175
Diluted net income per common share	$ 2.11	$ 1.59