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, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 1,285,370	$ 1,265,941	$ 1,285,370	$ 1,265,941	$ 1,280,870
Consumer, excluding credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	377,938	397,054	377,938	397,054	397,275
Consumer, excluding credit card | Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	3,083		3,083		3,466
Total retained loans	$ 311,338		$ 311,338		$ 326,409
Weighted average LTV ratio	47.00%		47.00%		49.00%
Weighted average FICO	774		774		770
Approximate percentage of Chapter 7 loans 30 days or more past due			9.00%
Interest income on nonaccrual loans recognized on a cash basis	$ 38	$ 44	$ 123	$ 133
Consumer, excluding credit card | Residential real estate | California
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	121,688		121,688		$ 127,072
Consumer, excluding credit card | Residential real estate | New York
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	47,198		47,198		48,815
Consumer, excluding credit card | Residential real estate | Florida
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	21,834		21,834		22,778
Consumer, excluding credit card | Residential real estate | Texas
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	14,638		14,638		15,506
Consumer, excluding credit card | Residential real estate | Massachusetts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	13,619		13,619		14,213
Consumer, excluding credit card | Residential real estate | Colorado
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	10,450		10,450		10,800
Consumer, excluding credit card | Residential real estate | Illinois
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	10,033		10,033		10,856
Consumer, excluding credit card | Residential real estate | Washington
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	9,415		9,415		9,923
Consumer, excluding credit card | Residential real estate | New Jersey
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	7,609		7,609		8,050
Consumer, excluding credit card | Residential real estate | Connecticut
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	6,879		6,879		7,163
Consumer, excluding credit card | Residential real estate | All other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	47,975		47,975		51,233
Consumer, excluding credit card | Residential real estate | No FICO/LTV available
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	830		830		989
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	72		72		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	0		0		0
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	146		146		223
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	5		5		4
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	4,949		4,949		6,491
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	75		75		102
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	296,443		296,443		309,251
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	$ 8,818		$ 8,818		$ 9,277