Loans - Consumer, Excluding Credit Card Loan Portfolio, Residential Real Estate, Nonaccrual Loans and Other Credit Quality Indicators (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 1,369,785	$ 1,285,370	$ 1,369,785	$ 1,285,370	$ 1,299,590
Consumer, excluding credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	369,859	377,938	369,859	377,938	376,334
Consumer, excluding credit card | Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	3,711		3,711		2,984
Total retained loans	$ 303,836		$ 303,836		$ 309,513
Weighted average LTV ratio	46.00%		46.00%		47.00%
Weighted average FICO	774		774		774
Approximate percentage of Chapter 7 loans 30 days or more past due			9.00%
Interest income on nonaccrual loans recognized on a cash basis	$ 35	$ 38	$ 109	$ 123
Consumer, excluding credit card | Residential real estate | California
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	117,880		117,880		$ 120,944
Consumer, excluding credit card | Residential real estate | New York
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	46,333		46,333		46,854
Consumer, excluding credit card | Residential real estate | Florida
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	21,735		21,735		21,820
Consumer, excluding credit card | Residential real estate | Texas
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	14,379		14,379		14,531
Consumer, excluding credit card | Residential real estate | Massachusetts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	13,131		13,131		13,511
Consumer, excluding credit card | Residential real estate | Colorado
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	10,412		10,412		10,465
Consumer, excluding credit card | Residential real estate | Washington
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	9,366		9,366		9,372
Consumer, excluding credit card | Residential real estate | Illinois
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	9,294		9,294		9,835
Consumer, excluding credit card | Residential real estate | New Jersey
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	7,431		7,431		7,554
Consumer, excluding credit card | Residential real estate | Connecticut
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	6,833		6,833		6,854
Consumer, excluding credit card | Residential real estate | All other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	47,042		47,042		47,773
Consumer, excluding credit card | Residential real estate | No FICO/LTV available
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	666		666		906
Consumer, excluding credit card | Residential real estate | Greater than 125% and refreshed FICO scores | Equal to or greater than 660
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	55		55		72
Consumer, excluding credit card | Residential real estate | Greater than 125% and refreshed FICO scores | Less than 660
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	3		3		3
Consumer, excluding credit card | Residential real estate | 101% to 125% and refreshed FICO scores | Equal to or greater than 660
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	211		211		161
Consumer, excluding credit card | Residential real estate | 101% to 125% and refreshed FICO scores | Less than 660
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	18		18		5
Consumer, excluding credit card | Residential real estate | 80% to 100% and refreshed FICO scores | Equal to or greater than 660
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	8,375		8,375		4,962
Consumer, excluding credit card | Residential real estate | 80% to 100% and refreshed FICO scores | Less than 660
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	129		129		73
Consumer, excluding credit card | Residential real estate | Lower than 80% and refreshed FICO scores | Equal to or greater than 660
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	286,009		286,009		294,797
Consumer, excluding credit card | Residential real estate | Lower than 80% and refreshed FICO scores | Less than 660
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 8,370		$ 8,370		$ 8,534