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Derivative Financial Instruments - Impact on Derivatives and Hedged Items on Consolidated Statement of Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income	$ (63)	$ (30)	$ (144)	$ 12
Amount of Gain (Loss) on Hedged Item Recognized in Consolidated Statement of Income	63	30	144	(11)
Net unrealized (losses) gains on AFS investment securities designated in fair value hedges	(110)	(43)	(320)	32
Foreign exchange contracts
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income			(1)	5
Amount of Gain (Loss) on Hedged Item Recognized in Consolidated Statement of Income			1	(5)
Interest Rate Contract One
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income			(388)	43
Amount of Gain (Loss) on Hedged Item Recognized in Consolidated Statement of Income			388	(42)
Interest Rate Contract Two
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income			245	(36)
Amount of Gain (Loss) on Hedged Item Recognized in Consolidated Statement of Income			$ (245)	$ 36
Net interest income \| Interest rate contracts \| Available-for-sale securities
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income	(154)	(59)
Amount of Gain (Loss) on Hedged Item Recognized in Consolidated Statement of Income	154	59
Net interest income \| Interest rate contracts \| Long-term debt
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income	95	24
Amount of Gain (Loss) on Hedged Item Recognized in Consolidated Statement of Income	(95)	(24)
Other fee revenue \| Interest rate contracts \| Available-for-sale securities
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income	(4)	5
Amount of Gain (Loss) on Hedged Item Recognized in Consolidated Statement of Income	$ 4	$ (5)