Earnings Per Common Share (EPS) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2021		Jun. 30, 2020		Jun. 30, 2021		Jun. 30, 2020
Basic and diluted:
Net income	$ 2,280		$ 257		$ 4,515		$ 624
Preferred dividends	(15)		(17)		(29)		(49)
Net income available to common shareholders	2,265		240		4,486		575
Earnings allocated to participating share awards	(16)		(2)		(31)		(4)
Net income attributable to common shareholders	$ 2,249		$ 238		$ 4,455		$ 571
Denominator:
Basic: Weighted-average common stock (in shares)	801,000		804,000		802,000		806,000
Add: Weighted-average stock options (in shares)	1,000		1,000		1,000		1,000
Diluted (in shares)	802,000		805,000		803,000		807,000
Basic EPS (in dollars per share)	$ 2.81	[1]	$ 0.29	[1]	$ 5.55	[2]	$ 0.71	[2]
Diluted EPS (in dollars per share)	$ 2.80	[1]	$ 0.29	[1]	$ 5.54	[2]	$ 0.71	[2]
Stock options
Denominator:
The dilutive effect of securities excluded from the calculation of earnings per share (in shares)	10		1,510		210		590

[1] Represents net income less (i) earnings allocated to participating share awards of $16 million and $2 million for the three months ended June 30, 2021 and 2020, respectively, and (ii) dividends on preferred shares of $15 million and $17 million for the three months ended June 30, 2021 and 2020, respectively.

[2] Represents net income less (i) earnings allocated to participating share awards of $31 million and $4 million for the six months ended June 30, 2021 and 2020, respectively, and (ii) dividends on preferred shares of $29 million and $49 million for the six months ended June 30, 2021 and 2020, respectively.