Loans - Consumer, Excluding Credit Card Loan Portfolio, Residential Real Estate (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 1,018,397	$ 1,010,206	$ 948,642
Consumer, excluding credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	296,161	295,556	$ 302,392
Consumer, excluding credit card | 30 or more days past due | U.S. government-guaranteed
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	35	31
Consumer, excluding credit card | Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans originated in 2022/2021	12,972	68,755
Term loans originated in 2021/2020	69,023	48,368
Term loans originated in 2020/2019	46,209	18,476
Term loans originated in 2019/2018	17,046	7,981
Term loans originated in 2018/2017	7,245	11,739
Term loans originated prior to 2018/2017	57,845	50,794
Revolving loans within the revolving period	6,001	6,409
Revolving loans converted to term loans	11,585	12,273
Total retained loans	$ 227,926	$ 224,795
% of 30 plus days past due to total retained loans, Term loans originated in 2022/2021	0.00%	0.02%
% of 30 plus days past due to total retained loans, Term loans originated in 2021/2020	0.02%	0.07%
% of 30 plus days past due to total retained loans, Term loans originated in 2020/2019	0.04%	0.26%
% of 30 plus days past due to total retained loans, Term loans originated in 2019/2018	0.18%	0.65%
% of 30 plus days past due to total retained loans, Term loans originated in 2018/2017	0.52%	0.47%
% of 30 plus days past due to total retained loans, Term loans originated prior to 2018/2017	2.43%	3.18%
% of 30 plus days past due to total retained loans, Revolving loans within the revolving period	0.33%	0.27%
% of 30 plus days past due to total retained loans, Revolving loans converted to term loans	3.44%	3.80%
% of 30 plus days past due to total retained loans	0.85%	1.02%
Consumer, excluding credit card | Residential real estate | Senior lien
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of total revolving loans that are senior lien loans	37.00%
Consumer, excluding credit card | Residential real estate | U.S. government-guaranteed
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 65	$ 66
Consumer, excluding credit card | Residential real estate | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans originated in 2022/2021	12,972	68,742
Term loans originated in 2021/2020	69,009	48,334
Term loans originated in 2020/2019	46,191	18,428
Term loans originated in 2019/2018	17,016	7,929
Term loans originated in 2018/2017	7,207	11,684
Term loans originated prior to 2018/2017	56,403	49,147
Revolving loans within the revolving period	5,981	6,392
Revolving loans converted to term loans	11,186	11,807
Total retained loans	225,965	222,463
Consumer, excluding credit card | Residential real estate | Current | U.S. government-guaranteed
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	30	35
Consumer, excluding credit card | Residential real estate | 30–149 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans originated in 2022/2021	0	13
Term loans originated in 2021/2020	13	23
Term loans originated in 2020/2019	9	27
Term loans originated in 2019/2018	13	27
Term loans originated in 2018/2017	23	22
Term loans originated prior to 2018/2017	630	578
Revolving loans within the revolving period	12	11
Revolving loans converted to term loans	164	182
Total retained loans	864	883
Consumer, excluding credit card | Residential real estate | 30–149 days past due | U.S. government-guaranteed
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	13	11
Consumer, excluding credit card | Residential real estate | 150 or more days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans originated in 2022/2021	0	0
Term loans originated in 2021/2020	1	11
Term loans originated in 2020/2019	9	21
Term loans originated in 2019/2018	17	25
Term loans originated in 2018/2017	15	33
Term loans originated prior to 2018/2017	812	1,069
Revolving loans within the revolving period	8	6
Revolving loans converted to term loans	235	284
Total retained loans	1,097	1,449
Consumer, excluding credit card | Residential real estate | 150 or more days past due | U.S. government-guaranteed
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 22	$ 20