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, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Earnings Per Share [Abstract]
Net income	$ 149	$ 136	$ 313	$ 405
Income allocated to participating securities	1	2	3	5
Net income attributable to common shares	$ 148	$ 134	$ 310	$ 400
Basic average common shares	171	176	173	176
Basic net income per common share	$ 0.87	$ 0.76	$ 1.80	$ 2.27
Basic average common shares	171	176	173	176
Net effect of the assumed exercise of stock options	2	2	1	2
Net effect of the assumed exercise of warrants	3	3	2	4
Diluted average common shares	176	181	176	182
Diluted net income per common share	$ 0.84	$ 0.74	$ 1.76	$ 2.20