Investment Securities - Investment Securities by Contractual Maturity (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Amortized Cost
AFS securities: Amortized cost, total	$ 103,970	$ 108,055
HTM securities: Net carrying amount, total	83,918
Investment securities: Amortized cost, total	187,888	179,826
Fair Value
AFS securities: Fair value, total	105,288	110,383
HTM securities: Fair value, total	84,099	74,420
Investment securities: Fair value, total	$ 189,387	184,803
Annualized Average Yield
AFS securities: Annualized average yield, total (as a percent)	1.40%
HTM securities: Annualized average yield, total (as a percent)	1.80%
Investment securities: Annualized average yield, total (as a percent)	1.60%
U.S. Treasury securities
Amortized Cost
AFS securities: Amortized cost, due within 1 year	$ 12,458
AFS securities: Amortized cost, after 1 year through 5 years	24,474
AFS securities: Amortized cost, after 5 years through 10 years	12,729
AFS securities: Amortized cost, total	49,661	45,345
HTM securities: Net carrying amount, due within 1 year	3,148
HTM securities: Net carrying amount, after 1 year through 5 years	18,837
HTM securities: Net carrying amount, after 5 year through 10 years	6,322
HTM securities: Net carrying amount, after 10 years	1,380
HTM securities: Net carrying amount, total	29,687
Fair Value
AFS securities: Fair value, due within 1 year	12,530
AFS securities: Fair value, after 1 year through 5 years	25,043
AFS securities: Fair value, after 5 years through 10 years	12,799
AFS securities: Fair value, total	50,372	46,355
HTM securities: Fair value, due within 1 year	3,184
HTM securities: Fair value, after 1 year through 5 years	19,494
HTM securities: Fair value, after 5 years through 10 years	6,740
HTM securities: Fair value, after 10 years	1,381
HTM securities: Fair value, total	$ 30,799	31,239
Annualized Average Yield
AFS securities: Annualized average yield, due within 1 year (as a percent)	1.20%
AFS securities: Annualized average yield, after 1 year through 5 years (as a percent)	1.40%
AFS securities: Annualized average yield, after 5 years through 10 years (as a percent)	1.00%
HTM securities: Annualized average yield, due within 1 year (as a percent)	2.00%
HTM securities: Annualized average yield, after 1 years through 5 years (as a percent)	1.70%
HTM securities: Annualized average yield, after 5 years through 10 years (as a percent)	2.30%
HTM securities: Annualized average yield, after 10 year (as a percent)	2.20%
U.S. agency securities
Amortized Cost
AFS securities: Amortized cost, due within 1 year	$ 3
AFS securities: Amortized cost, after 1 year through 5 years	142
AFS securities: Amortized cost, after 5 years through 10 years	1,314
AFS securities: Amortized cost, after 10 years	31,104
AFS securities: Amortized cost, total	32,563	37,389
HTM securities: Net carrying amount, after 5 year through 10 years	601
HTM securities: Net carrying amount, after 10 years	50,197
HTM securities: Net carrying amount, total	50,798
Fair Value
AFS securities: Fair value, due within 1 year	3
AFS securities: Fair value, after 1 year through 5 years	146
AFS securities: Fair value, after 5 years through 10 years	1,347
AFS securities: Fair value, after 10 years	31,330
AFS securities: Fair value, total	32,826	38,126
HTM securities: Fair value, after 5 years through 10 years	620
HTM securities: Fair value, after 10 years	49,263
HTM securities: Fair value, total	$ 49,883	39,647
Annualized Average Yield
AFS securities: Annualized average yield, due within 1 year (as a percent)	1.50%
AFS securities: Annualized average yield, after 1 year through 5 years (as a percent)	1.50%
AFS securities: Annualized average yield, after 5 years through 10 years (as a percent)	1.80%
AFS securities: Annualized average yield, after 10 years (as a percent)	1.60%
HTM securities: Annualized average yield, after 5 years through 10 years (as a percent)	2.00%
HTM securities: Annualized average yield, after 10 year (as a percent)	1.70%
Agency CMBS
Amortized Cost
AFS securities: Amortized cost, due within 1 year	$ 65
AFS securities: Amortized cost, after 1 year through 5 years	948
AFS securities: Amortized cost, after 5 years through 10 years	12,812
AFS securities: Amortized cost, after 10 years	3,796
AFS securities: Amortized cost, total	17,621	19,982
HTM securities: Net carrying amount, due within 1 year	21
HTM securities: Net carrying amount, after 1 year through 5 years	1,060
HTM securities: Net carrying amount, after 5 year through 10 years	1,216
HTM securities: Net carrying amount, after 10 years	243
HTM securities: Net carrying amount, total	2,540
Fair Value
AFS securities: Fair value, due within 1 year	65
AFS securities: Fair value, after 1 year through 5 years	964
AFS securities: Fair value, after 5 years through 10 years	13,123
AFS securities: Fair value, after 10 years	3,747
AFS securities: Fair value, total	17,899	20,438
HTM securities: Fair value, due within 1 year	21
HTM securities: Fair value, after 1 year through 5 years	1,056
HTM securities: Fair value, after 5 years through 10 years	1,191
HTM securities: Fair value, after 10 years	230
HTM securities: Fair value, total	$ 2,498	2,634
Annualized Average Yield
AFS securities: Annualized average yield, due within 1 year (as a percent)	2.00%
AFS securities: Annualized average yield, after 1 year through 5 years (as a percent)	1.30%
AFS securities: Annualized average yield, after 5 years through 10 years (as a percent)	1.50%
AFS securities: Annualized average yield, after 10 years (as a percent)	1.20%
HTM securities: Annualized average yield, due within 1 year (as a percent)	2.40%
HTM securities: Annualized average yield, after 1 years through 5 years (as a percent)	1.40%
HTM securities: Annualized average yield, after 5 years through 10 years (as a percent)	1.20%
HTM securities: Annualized average yield, after 10 year (as a percent)	1.50%
Non-agency CMBS
Amortized Cost
HTM securities: Net carrying amount, due within 1 year	$ 153
HTM securities: Net carrying amount, after 1 year through 5 years	51
HTM securities: Net carrying amount, after 5 year through 10 years	633
HTM securities: Net carrying amount, after 10 years	56
HTM securities: Net carrying amount, total	893
Fair Value
HTM securities: Fair value, due within 1 year	153
HTM securities: Fair value, after 1 year through 5 years	52
HTM securities: Fair value, after 5 years through 10 years	656
HTM securities: Fair value, after 10 years	58
HTM securities: Fair value, total	$ 919	900
Annualized Average Yield
HTM securities: Annualized average yield, due within 1 year (as a percent)	4.50%
HTM securities: Annualized average yield, after 1 years through 5 years (as a percent)	2.70%
HTM securities: Annualized average yield, after 5 years through 10 years (as a percent)	3.70%
HTM securities: Annualized average yield, after 10 year (as a percent)	4.00%
Corporate bonds
Amortized Cost
AFS securities: Amortized cost, due within 1 year	$ 397
AFS securities: Amortized cost, after 1 year through 5 years	1,147
AFS securities: Amortized cost, after 5 years through 10 years	97
AFS securities: Amortized cost, after 10 years	10
AFS securities: Amortized cost, total	1,651	1,694
Fair Value
AFS securities: Fair value, due within 1 year	400
AFS securities: Fair value, after 1 year through 5 years	1,174
AFS securities: Fair value, after 5 years through 10 years	99
AFS securities: Fair value, after 10 years	10
AFS securities: Fair value, total	$ 1,683	1,736
Annualized Average Yield
AFS securities: Annualized average yield, due within 1 year (as a percent)	2.40%
AFS securities: Annualized average yield, after 1 year through 5 years (as a percent)	2.70%
AFS securities: Annualized average yield, after 5 years through 10 years (as a percent)	2.20%
AFS securities: Annualized average yield, after 10 years (as a percent)	1.60%
State and municipal securities
Amortized Cost
AFS securities: Amortized cost, due within 1 year	$ 3
AFS securities: Amortized cost, after 1 year through 5 years	16
AFS securities: Amortized cost, after 5 years through 10 years	24
AFS securities: Amortized cost, after 10 years	135
AFS securities: Amortized cost, total	178	1,461
Fair Value
AFS securities: Fair value, due within 1 year	3
AFS securities: Fair value, after 1 year through 5 years	17
AFS securities: Fair value, after 5 years through 10 years	33
AFS securities: Fair value, after 10 years	158
AFS securities: Fair value, total	$ 211	1,563
Annualized Average Yield
AFS securities: Annualized average yield, due within 1 year (as a percent)	1.80%
AFS securities: Annualized average yield, after 1 year through 5 years (as a percent)	2.20%
AFS securities: Annualized average yield, after 5 years through 10 years (as a percent)	2.40%
AFS securities: Annualized average yield, after 10 years (as a percent)	4.40%
FFELP Student Loan ABS
Amortized Cost
AFS securities: Amortized cost, due within 1 year	$ 33
AFS securities: Amortized cost, after 1 year through 5 years	73
AFS securities: Amortized cost, after 5 years through 10 years	216
AFS securities: Amortized cost, after 10 years	1,644
AFS securities: Amortized cost, total	1,966	1,735
Fair Value
AFS securities: Fair value, due within 1 year	32
AFS securities: Fair value, after 1 year through 5 years	72
AFS securities: Fair value, after 5 years through 10 years	212
AFS securities: Fair value, after 10 years	1,651
AFS securities: Fair value, total	$ 1,967	1,716
Annualized Average Yield
AFS securities: Annualized average yield, due within 1 year (as a percent)	0.80%
AFS securities: Annualized average yield, after 1 year through 5 years (as a percent)	0.80%
AFS securities: Annualized average yield, after 5 years through 10 years (as a percent)	0.80%
AFS securities: Annualized average yield, after 10 years (as a percent)	1.10%
Other ABS
Amortized Cost
AFS securities: Amortized cost, after 1 year through 5 years	$ 330
AFS securities: Amortized cost, total	330	449
Fair Value
AFS securities: Fair value, after 1 year through 5 years	330
AFS securities: Fair value, total	$ 330	$ 449
Annualized Average Yield
AFS securities: Annualized average yield, after 1 year through 5 years (as a percent)	0.40%