Earnings per Common Share (Schedule of Basic and Diluted Earnings per Common Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	$ 280	$ 261	$ 747	$ 865
Dividends, Preferred Stock, Cash	0	0	0	(30)
Net Income (Loss) from Continuing Operations Available to Common Shareholders, Basic	280	261	747	835
Net Income (Loss) from Continuing Operations Available to Common Shareholders, Diluted	280	261	747	835
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	2	(52)	1	(46)
Net Income (Loss) Available to Common Stockholders, Basic	282	209	748	789
Net Income (Loss) Available to Common Stockholders, Diluted	$ 282	$ 209	$ 748	$ 789
Weighted Average Number of Shares Outstanding, Basic	449,169	482,393	457,612	483,993
Weighted Average Number of Shares Outstanding, Diluted	451,078	483,575	458,848	484,762
Earnings Per Share, Basic [Abstract]
Income (Loss) from Continuing Operations, Per Basic Share	$ 0.62	$ 0.54	$ 1.63	$ 1.73
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share	0.00	(0.11)	0.00	(0.10)
Earnings Per Share, Basic	0.63	0.43	1.63	1.63
Earnings Per Share, Diluted [Abstract]
Income (Loss) from Continuing Operations, Per Diluted Share	0.62	0.54	1.63	1.72
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share	0.00	(0.11)	0.00	(0.10)
Earnings Per Share, Diluted	$ 0.63	$ 0.43	$ 1.63	$ 1.63