Loans - Consumer, Excluding Credit Card Loan Portfolio, Residential Real Estate (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 963,665	$ 960,506	$ 965,448
Consumer, excluding credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	297,731	302,127	$ 307,005
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	32	40
Consumer, excluding credit card | Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans originated in 2021/2020	31,269	56,588
Term loans originated in 2020/2019	54,751	31,859
Term loans originated in 2019/2018	23,893	13,930
Term loans originated in 2018/2017	10,140	20,450
Term loans originated in 2017/2016	15,027	28,025
Term loans originated prior to 2017/2016	62,035	50,736
Revolving loans within the revolving period	5,735	7,413
Revolving loans converted to term loans	15,181	16,301
Total retained loans	$ 218,031	$ 225,302
% of 30 plus days past due to total retained loans, Term loans originated in 2021/2020	0.04%	0.02%
% of 30 plus days past due to total retained loans, Term loans originated in 2020/2019	0.01%	0.12%
% of 30 plus days past due to total retained loans, Term loans originated in 2019/2018	0.08%	0.22%
% of 30 plus days past due to total retained loans, Term loans originated in 2018/2017	0.18%	0.20%
% of 30 plus days past due to total retained loans, Term loans originated in 2017/2016	0.21%	0.17%
% of 30 plus days past due to total retained loans, Term loans originated prior to 2017/2016	2.25%	2.91%
% of 30 plus days past due to total retained loans, Revolving loans within the revolving period	0.21%	0.58%
% of 30 plus days past due to total retained loans, Revolving loans converted to term loans	3.00%	3.12%
% of 30 plus days past due to total retained loans	0.89%	0.98%
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	36.00%
Consumer, excluding credit card | Residential real estate | U.S. government-guaranteed
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 72	$ 76
Consumer, excluding credit card | Residential real estate | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans originated in 2021/2020	31,258	56,576
Term loans originated in 2020/2019	54,745	31,820
Term loans originated in 2019/2018	23,873	13,900
Term loans originated in 2018/2017	10,122	20,410
Term loans originated in 2017/2016	14,996	27,978
Term loans originated prior to 2017/2016	60,605	49,218
Revolving loans within the revolving period	5,723	7,370
Revolving loans converted to term loans	14,726	15,792
Total retained loans	216,048	223,064
Consumer, excluding credit card | Residential real estate | Current | U.S. government-guaranteed
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	40	36
Consumer, excluding credit card | Residential real estate | 30–149 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans originated in 2021/2020	11	9
Term loans originated in 2020/2019	4	25
Term loans originated in 2019/2018	16	20
Term loans originated in 2018/2017	13	22
Term loans originated in 2017/2016	13	29
Term loans originated prior to 2017/2016	539	674
Revolving loans within the revolving period	9	21
Revolving loans converted to term loans	185	245
Total retained loans	790	1,045
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	11	16
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 2021/2020	0	3
Term loans originated in 2020/2019	2	14
Term loans originated in 2019/2018	4	10
Term loans originated in 2018/2017	5	18
Term loans originated in 2017/2016	18	18
Term loans originated prior to 2017/2016	891	844
Revolving loans within the revolving period	3	22
Revolving loans converted to term loans	270	264
Total retained loans	1,193	1,193
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	$ 21	$ 24