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		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Net income	$ 318	$ 226	$ 925	$ 631
Income allocated to participating securities	2	2	6	5
Net income attributable to common shares	$ 316	$ 224	$ 919	$ 626
Basic average common shares	167	174	170	175
Basic net income per common share	$ 1.89	$ 1.29	$ 5.41	$ 3.58
Basic average common shares	167	174	170	175
Net effect of the assumed exercise of stock options	2	2	2	3
Net effect of the assumed exercise of warrants	1	1	1	1
Diluted average common shares	170	177	173	179
Diluted net income per common share	$ 1.86	$ 1.26	$ 5.32	$ 3.50