Earnings Per Common Share (EPS) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2020		Sep. 30, 2019		Sep. 30, 2020		Sep. 30, 2019
Basic and diluted:
Net income	$ 1,073		$ 1,755		$ 1,697		$ 5,066
Preferred dividends	(16)		(21)		(65)		(61)
Net income available to common shareholders	1,057		1,734		1,632		5,005
Earnings allocated to participating share awards	(7)		(11)		(10)		(35)
Net income attributable to common shareholders	$ 1,050		$ 1,723		$ 1,622		$ 4,970
Denominator:
Basic: Weighted-average common stock (in shares)	804.0		825.0		805.0		833.0
Add: Weighted-average stock options (in shares)	1.0		2.0		1.0		2.0
Diluted (in shares)	805.0		827.0		806.0		835.0
Basic EPS (in dollars per share)	$ 1.31	[1]	$ 2.09	[1]	$ 2.01	[2]	$ 5.97	[2]
Diluted EPS (in dollars per share)	$ 1.30	[1]	$ 2.08	[1]	$ 2.01	[2]	$ 5.95	[2]
Stock options [Member]
Denominator:
The dilutive effect of securities excluded from the calculation of earnings per share (in shares)	0.9		0.0		0.6		0.3

[1] Represents net income less (i) earnings allocated to participating share awards of $7 million and $11 million for the three months ended September 30, 2020 and 2019, respectively, and (ii) dividends on preferred shares of $16 million and $21 million for the three months ended September 30, 2020 and 2019, respectively.

[2] Represents net income less (i) earnings allocated to participating share awards of $10 million and $35 million for the nine months ended September 30, 2020 and 2019, respectively, and (ii) dividends on preferred shares of $65 million and $61 million for the nine months ended September 30, 2020 and 2019, respectively.