Earnings per Common Share (Schedule of Basic and Diluted Earnings per Common Share) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	$ 246	$ 261	$ 357	$ 247	$ 276	$ 273	$ 169	$ 179	$ 1,111	$ 897	$ 925
Dividends, Preferred Stock, Cash									(30)	(2,571)	(268)
Net income (loss) from continuing operations attributable to common shareholders									1,081	(1,674)	657
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	$ 2	$ (52)	$ 3	$ 3	$ (13)	$ (5)	$ 13	$ 397	(44)	392	225
Net Income (Loss) Available to Common Stockholders, Basic									$ 1,037	$ (1,282)	$ 882
Weighted Average Number of Shares Outstanding, Basic									481,104,533	482,873	481,155
Weighted Average Number of Shares Outstanding, Diluted									482,182,115	482,873	481,934
Stock Repurchase and Redemption Premium										$ 2,364
Earnings Per Share, Basic [Abstract]
Income (Loss) from Continuing Operations, Per Basic Share	$ 0.52	$ 0.54	$ 0.70	$ 0.48	$ (1.94)	$ 0.49	$ (2.24)	$ 0.23	$ 2.25	$ (3.47)	$ 1.36
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share	0.53	0.43	0.71	0.49	(1.97)	0.48	(2.22)	1.06	(0.09)	0.81	0.47
Earnings Per Share, Basic									2.15	(2.66)	1.83
Earnings Per Share, Diluted [Abstract]
Income (Loss) from Continuing Operations, Per Diluted Share	0.52	0.54	0.70	0.48	(1.94)	0.49	(2.24)	0.23	2.24	(3.47)	1.36
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share	$ 0.52	$ 0.43	$ 0.71	$ 0.49	$ (1.97)	$ 0.47	$ (2.22)	$ 1.06	(0.09)	0.81	0.47
Earnings Per Share, Diluted									$ 2.15	$ (2.66)	$ 1.83