Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income		$ 1,526	$ 698	$ 4,275	$ 2,164
Preferred stock dividends and other		(120)	(83)	(364)	(171)
Net Income Available to Common Stockholders		$ 1,406	$ 615	$ 3,911	$ 1,993
Weighted-average common shares outstanding - basic (in shares)		1,888	1,289	1,885	1,288
Basic earnings per share (USD per share)	[1]	$ 0.74	$ 0.48	$ 2.07	$ 1.55
Weighted-average common shares outstanding - diluted (in shares)		1,898	1,294	1,895	1,294
Diluted earnings per share (USD per share)	[1]	$ 0.74	$ 0.48	$ 2.06	$ 1.54
Antidilutive stock options and restricted stock awards excluded from the calculation of diluted EPS (in shares)		13	19	15	20
Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income		$ 1,462	$ 698	$ 4,096	$ 2,164
Preferred stock dividends and other		(115)	(83)	(349)	(171)
Net Income Available to Common Stockholders		$ 1,347	$ 615	$ 3,747	$ 1,993
Weighted-average common shares outstanding - basic (in shares)		1,809	1,289	1,806	1,288
Basic earnings per share (USD per share)		$ 0.74	$ 0.48	$ 2.07	$ 1.55
Reallocation of net income available to common stockholders as a result of conversion of nonvoting to voting shares		$ 59		$ 164
Allocation of net income available to common stockholders:		$ 1,406	$ 615	$ 3,911	$ 1,993
Conversion of nonvoting shares to voting shares (in shares)		79		79
Common stock equivalent shares related to stock incentive plans (shares)		10	5	10	6
Weighted-average common shares outstanding - diluted (in shares)		1,898	1,294	1,895	1,294
Diluted earnings per share (USD per share)		$ 0.74	$ 0.48	$ 2.06	$ 1.54
Nonvoting Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income		$ 64		$ 179
Preferred stock dividends and other		(5)		(15)
Net Income Available to Common Stockholders		$ 59		$ 164
Weighted-average common shares outstanding - basic (in shares)		79		79
Basic earnings per share (USD per share)		$ 0.74		$ 2.07
Reallocation of net income available to common stockholders as a result of conversion of nonvoting to voting shares		$ 0		$ 0
Allocation of net income available to common stockholders:		$ 59		$ 164
Conversion of nonvoting shares to voting shares (in shares)		0		0
Common stock equivalent shares related to stock incentive plans (shares)		0		0
Weighted-average common shares outstanding - diluted (in shares)		79		79
Diluted earnings per share (USD per share)		$ 0.74		$ 2.06

[1] For the three and nine months ended September 30, 2021, the Company had voting and nonvoting common stock outstanding. As the participation rights, including dividend and liquidation rights, are identical between the voting and nonvoting stock classes, basic and diluted earnings per share are the same for each class. See Note 16 for additional information.