Earnings Per Common Share (EPS) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020
Basic and diluted:
Net income		$ 2,235	$ 367
Preferred dividends		(14)	(32)
Net income available to common shareholders		2,221	335
Earnings allocated to participating share awards		(15)	(2)
Net income attributable to common shareholders		$ 2,206	$ 333
Denominator:
Basic: Weighted-average common stock (in shares)		804.0	807.0
Add: Weighted-average stock options (in shares)		1.0	1.0
Diluted (in shares)		805.0	808.0
Basic EPS (in dollars per share)	[1]	$ 2.74	$ 0.41
Diluted EPS (in dollars per share)	[1]	$ 2.74	$ 0.41
Stock options
Denominator:
The dilutive effect of securities excluded from the calculation of earnings per share (in shares)		0.3	0.3

[1] Represents net income less (i) earnings allocated to participating share awards of $15 million and $2 million for the three months ended March 31, 2021 and 2020, respectively, and (ii) dividends on preferred shares of $14 million and $32 million for the three months ended March 31, 2021 and 2020, respectively.