Earnings Per Common Share (EPS) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Basic and diluted:
Net income		$ 2,010	$ 1,654	$ 1,623	$ 1,634	$ (1,206)	$ 1,359	$ 1,344	$ 1,251	$ 6,921	$ 2,748	$ 5,375
Dividends Preferred Stock		(19)	(20)	(20)	(21)	(20)	(21)	(19)	(21)	(80)	(81)	(80)
Net income available to common shareholders										6,841	2,667	5,295
Earnings allocated to participating share awards		$ (16)	$ (13)	$ (12)	$ (13)	$ (2)	$ (11)	$ (11)	$ (10)	(54)	(21)	(43)
Net income attributable to common shareholders										$ 6,787	$ 2,646	$ 5,252
Denominator:
Basic: Weighted-average common stock										856.0	883.0	933.0
Add: Weighted-average stock options										3.0	3.0	2.0
Diluted										859.0	886.0	935.0
Basic EPS:
Basic	[1]									$ 7.93	$ 3	$ 5.63
Diluted EPS:
Diluted	[1]									$ 7.91	$ 2.99	$ 5.61
Stock Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per Share, amount										0.7	0.6	2.4

[1] Represents net income less (i) earnings allocated to participating share awards of $ 54 million, $ 21 million and $ 43 million for the years ended December 31, 2018 , 2017 and 2016 , respectively, and (ii) dividends on preferred shares of $ 80 millio n, $ 81 million and $ 80 million for the years ended December 31, 2018 , 2017 and 2016 , r e s p e c t i v e l y .