Derivative Financial Instruments - Impact on Derivatives and Hedged Items on Consolidated Statement of Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income	$ 40	$ (82)
Amount of Gain (Loss) on Hedged Item Recognized in Consolidated Statement of Income	(40)	81
Net unrealized losses on AFS investment securities designated in fair value hedges	105	210
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	(63)	150
Amount of Gain (Loss) on Hedged Item Recognized in Consolidated Statement of Income	63	(150)
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	126	(235)
Amount of Gain (Loss) on Hedged Item Recognized in Consolidated Statement of Income	(126)	234
Other fee revenue | Foreign exchange 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	(23)	3
Amount of Gain (Loss) on Hedged Item Recognized in Consolidated Statement of Income	$ 23	$ (3)