Earnings Per Common Share (EPS) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Basic and diluted:
Net income		$ 367	$ 1,550
Preferred dividends		(32)	(21)
Net income available to common shareholders		335	1,529
Earnings allocated to participating share awards		(2)	(11)
Net income attributable to common shareholders		$ 333	$ 1,518
Denominator:
Basic: Weighted-average common stock (in shares)		807.0	841.0
Add: Weighted-average stock options (in shares)		1.0	2.0
Diluted (in shares)		808.0	843.0
Basic EPS (in dollars per share)	[1]	$ 0.41	$ 1.81
Diluted EPS (in dollars per share)	[1]	$ 0.41	$ 1.80
Stock options [Member]
Denominator:
The dilutive effect of securities excluded from the calculation of earnings per share (in shares)		0.3	0.9

[1] Represents net income less (i) earnings allocated to participating share awards of $2 million and $11 million for the three months ended March 31, 2020 and 2019, respectively, and (ii) dividends on preferred shares of $32 million and $21 million for the three months ended March 31, 2020 and 2019, respectively.