Derivative Financial Instruments - Carrying Value of Hedged Items in Fair Value Hedge (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Derivatives, Fair Value [Line Items]
Carrying amount of hedged items	$ 15,724	$ 11,685
Active hedged asset adjustments	(927)	(1,283)
Discontinued hedged asset adjustments	(208)	(232)
Total hedged asset adjustments	$ (1,135)	$ (1,515)
Hedged Asset, Statement of Financial Position [Extensible Enumeration]	Securities available-for-sale (amortized cost of $31.8 billion and $27.2 billion at September 30, 2025 and December 31, 2024, respectively, and includes $1.9 billion and $0.6 billion pledged to creditors at September 30, 2025 and December 31, 2024, respectively)	Securities available-for-sale (amortized cost of $31.8 billion and $27.2 billion at September 30, 2025 and December 31, 2024, respectively, and includes $1.9 billion and $0.6 billion pledged to creditors at September 30, 2025 and December 31, 2024, respectively)
Deposits
Derivatives, Fair Value [Line Items]
Carrying amount of hedged liability items	$ 1,493	$ 1,476
Active hedged liability adjustments	(21)	(61)
Discontinued hedged liability adjustments	14	37
Total hedged liability adjustments	$ (7)	$ (24)
Hedged Liability, Statement of Financial Position [Extensible Enumeration]	Deposits	Deposits
Long-term debt
Derivatives, Fair Value [Line Items]
Carrying amount of hedged liability items	$ 8,839	$ 8,236
Active hedged liability adjustments	(61)	(295)
Discontinued hedged liability adjustments	0	31
Total hedged liability adjustments	$ (61)	$ (264)
Hedged Liability, Statement of Financial Position [Extensible Enumeration]	Long-term debt (includes $8.4 billion and $7.9 billion designated under fair value option at September 30, 2025 and December 31, 2024, respectively)	Long-term debt (includes $8.4 billion and $7.9 billion designated under fair value option at September 30, 2025 and December 31, 2024, respectively)