Loans - Consumer, Excluding Credit Card Loan Portfolio, Auto and Other (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 | Auto and other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans originated in 2022/2021	7,334	35,515
Term loans originated in 2021/2020	30,599	19,079
Term loans originated in 2020/2019	16,546	7,531
Term loans originated in 2019/2018	6,503	3,724
Term loans originated in 2018/2017	3,049	1,832
Term loans originated prior to 2018/2017	1,835	688
Revolving loans within the revolving period	2,240	2,259
Revolving loans converted to term loans	129	133
Total retained loans	$ 68,235	$ 70,761
% of 30 plus days past due to total retained loans, Term loans originated in 2022/2021	0.85%	0.54%
% of 30 plus days past due to total retained loans, Term loans originated in 2021/2020	0.52%	0.47%
% of 30 plus days past due to total retained loans, Term loans originated in 2020/2019	0.45%	1.17%
% of 30 plus days past due to total retained loans, Term loans originated in 2019/2018	1.05%	1.42%
% of 30 plus days past due to total retained loans, Term loans originated in 2018/2017	1.31%	1.75%
% of 30 plus days past due to total retained loans, Term loans originated prior to 2018/2017	1.91%	3.20%
% of 30 plus days past due to total retained loans, Revolving loans within the revolving period	0.76%	0.75%
% of 30 plus days past due to total retained loans, Revolving loans converted to term loans	9.30%	9.77%
% of 30 plus days past due to total retained loans	0.69%	0.71%
Consumer, excluding credit card | Auto and other | Paycheck Protection Program (PPP)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 2,900	$ 5,400
Current | Consumer, excluding credit card | Auto and other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans originated in 2022/2021	7,272	35,323
Term loans originated in 2021/2020	30,438	18,324
Term loans originated in 2020/2019	16,259	7,443
Term loans originated in 2019/2018	6,435	3,671
Term loans originated in 2018/2017	3,009	1,800
Term loans originated prior to 2018/2017	1,800	666
Revolving loans within the revolving period	2,223	2,242
Revolving loans converted to term loans	117	120
Total retained loans	67,553	69,589
Current | Consumer, excluding credit card | Auto and other | Paycheck Protection Program (PPP)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans originated in 2022/2021		4,400
Term loans originated in 2021/2020	2,500	1,000
Term loans originated in 2020/2019	353
30 or more days past due | Consumer, excluding credit card | Auto and other | Paycheck Protection Program (PPP)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	213	667
30–119 days past due | Consumer, excluding credit card | Auto and other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans originated in 2022/2021	62	192
Term loans originated in 2021/2020	161	720
Term loans originated in 2020/2019	124	88
Term loans originated in 2019/2018	68	53
Term loans originated in 2018/2017	40	31
Term loans originated prior to 2018/2017	34	21
Revolving loans within the revolving period	11	12
Revolving loans converted to term loans	6	6
Total retained loans	506	1,123
120 or more days past due | Consumer, excluding credit card | Auto and other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans originated in 2022/2021	0	0
Term loans originated in 2021/2020	0	35
Term loans originated in 2020/2019	163	0
Term loans originated in 2019/2018	0	0
Term loans originated in 2018/2017	0	1
Term loans originated prior to 2018/2017	1	1
Revolving loans within the revolving period	6	5
Revolving loans converted to term loans	6	7
Total retained loans	$ 176	$ 49