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Investment Securities - Additional Information (Details) - USD ($)				3 Months Ended		6 Months Ended
	Jun. 30, 2025	May 18, 2025	Dec. 31, 2024	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Debt Securities, Available-for-sale [Line Items]
Accrued interest receivable	$ 304,000,000		$ 262,000,000
Proceeds from sales of securities related to the Transaction				$ 9,700,000,000	$ 0	$ 9,696,000,000	$ 0
Investment securities	38,500,000,000		39,400,000,000	38,500,000,000		38,500,000,000
Securities received as collateral	$ 7,000,000		$ 18,000,000	$ 7,000,000		$ 7,000,000
Discover
Debt Securities, Available-for-sale [Line Items]
Business combination, recognized asset acquired, investment in debt and equity securities, current		$ 14,100,000,000
Business combination, recognized asset acquired, acquired debt securities sold		$ (9,700,000,000)
Investment securities available for sale | Government Contracts Concentration Risk | US Treasury and Agency securities
Debt Securities, Available-for-sale [Line Items]
Percentage of portfolio	97.00%		96.00%

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