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								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	$ 179	$ 280	$ 254	$ 213	$ 246	$ 261	$ 357	$ 247	$ 926	$ 1,111	$ 897
Dividends, Preferred Stock, Cash									0	(30)	(2,571)
Net Income (Loss) from Continuing Operations Available to Common Shareholders, Basic									926	1,081	(1,674)
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	$ 2	$ 2	$ (2)	$ 1	$ 2	$ (52)	$ 3	$ 3	3	(44)	392
Net Income (Loss) Available to Common Stockholders, Basic									$ 929	$ 1,037	$ (1,282)
Weighted Average Number of Shares Outstanding, Basic									453,704	481,105	482,873
Weighted Average Number of Shares Outstanding, Diluted									455,350	482,182	482,873
Net Income (Loss) from Continuing Operations Available to Common Shareholders, Diluted									$ 926	$ 1,081	$ (1,674)
Net Income (Loss) from Discontinued Operations Available to Common Shareholders, Diluted									3	(44)	392
Net Income (Loss) Available to Common Stockholders, Diluted									$ 929	$ 1,037	$ (1,282)
Earnings Per Share, Basic [Abstract]
Income (Loss) from Continuing Operations, Per Basic Share	$ 0.40	$ 0.62	$ 0.55	$ 0.46	$ 0.52	$ 0.54	$ 0.70	$ 0.48	$ 2.04	$ 2.25	$ (3.47)
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share									0.01	(0.09)	0.81
Earnings Per Share, Basic	0.41	0.63	0.55	0.46	0.53	0.43	0.71	0.49	2.05	2.15	(2.66)
Earnings Per Share, Diluted [Abstract]
Income (Loss) from Continuing Operations, Per Diluted Share	0.40	0.62	0.55	0.46	0.52	0.54	0.70	0.48	2.03	2.24	(3.47)
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share									0.01	(0.09)	0.81
Earnings Per Share, Diluted	$ 0.41	$ 0.63	$ 0.55	$ 0.46	$ 0.52	$ 0.43	$ 0.71	$ 0.49	$ 2.04	$ 2.15	$ (2.66)
Stock Redemption and Repurchase Premium											$ 2,364