Earnings Per Common Share (EPS) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2020		Jun. 30, 2019		Jun. 30, 2020		Jun. 30, 2019
Basic and diluted:
Net income	$ 257		$ 1,761		$ 624		$ 3,311
Preferred dividends	(17)		(19)		(49)		(40)
Net income available to common shareholders	240		1,742		575		3,271
Earnings allocated to participating share awards	(2)		(13)		(4)		(24)
Net income attributable to common shareholders	$ 238		$ 1,729		$ 571		$ 3,247
Denominator:
Basic: Weighted-average common stock (in shares)	804.0		834.0		806.0		837.0
Add: Weighted-average stock options (in shares)	1.0		2.0		1.0		2.0
Diluted (in shares)	805.0		836.0		807.0		839.0
Basic EPS (in dollars per share)	$ 0.29	[1]	$ 2.07	[1]	$ 0.71	[2]	$ 3.88	[2]
Diluted EPS (in dollars per share)	$ 0.29	[1]	$ 2.07	[1]	$ 0.71	[2]	$ 3.87	[2]
Stock options [Member]
Denominator:
The dilutive effect of securities excluded from the calculation of earnings per share (in shares)	1.5		0.4		0.6		0.4

[1] Represents net income less (i) earnings allocated to participating share awards of $2 million and $13 million for the three months ended June 30, 2020 and 2019, respectively, and (ii) dividends on preferred shares of $17 million and $19 million for the three months ended June 30, 2020 and 2019, respectively.

[2] Represents net income less (i) earnings allocated to participating share awards of $4 million and $24 million for the six months ended June 30, 2020 and 2019, respectively, and (ii) dividends on preferred shares of $49 million and $40 million for the six months ended June 30, 2020 and 2019, respectively.