Earnings per Common Share (Schedule of Basic and Diluted Earnings per Common Share) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Share [Abstract]
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	$ 254	$ 357	$ 467	$ 604
Dividends, Preferred Stock, Cash	0	(15)	0	(30)
Net income (loss) from continuing operations attributable to common shareholders	254	342	467	574
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	(2)	3	(1)	6
Net Income (Loss) Available to Common Stockholders, Basic	$ 252	$ 345	$ 466	$ 580
Weighted Average Number of Shares Outstanding, Basic	457,891	485,370	461,904	484,802
Weighted Average Number of Shares Outstanding, Diluted	458,819	486,074	462,802	485,364
Earnings Per Share, Basic [Abstract]
Income (Loss) from Continuing Operations, Per Basic Share	$ 0.55	$ 0.70	$ 1.01	$ 1.18
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share	(0.01)	0.01	0.00	0.01
Earnings Per Share, Basic	0.55	0.71	1.01	1.20
Earnings Per Share, Diluted [Abstract]
Income (Loss) from Continuing Operations, Per Diluted Share	0.55	0.70	1.01	1.18
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share	(0.01)	0.01	0.00	0.01
Earnings Per Share, Diluted	$ 0.55	$ 0.71	$ 1.01	$ 1.19