Derivative Financial Instruments - Carrying Value of Hedged Items in Fair Value Hedge (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Derivatives, Fair Value [Line Items]
Carrying amount of hedged items	$ 12,958	$ 11,112
Active hedged asset adjustments	(1,024)	(1,320)
Discontinued hedged asset adjustments	(41)	(70)
Total hedged asset adjustments	$ (1,065)	$ (1,390)
Hedged Asset, Statement of Financial Position [Extensible Enumeration]	Securities available-for-sale (includes amortized cost of $27.7 billion and $28.0 billion at September 30, 2024 and December 31, 2023, respectively, an allowance for credit losses of nil at both September 30, 2024 and December 31, 2023, and $1.6 billion and $0.2 billion pledged to creditors at September 30, 2024 and December 31, 2023, respectively)	Securities available-for-sale (includes amortized cost of $27.7 billion and $28.0 billion at September 30, 2024 and December 31, 2023, respectively, an allowance for credit losses of nil at both September 30, 2024 and December 31, 2023, and $1.6 billion and $0.2 billion pledged to creditors at September 30, 2024 and December 31, 2023, respectively)
Deposits
Derivatives, Fair Value [Line Items]
Carrying amount of hedged liability items	$ 1,483	$ 1,463
Active hedged liability adjustments	(62)	(104)
Discontinued hedged liability adjustments	44	67
Total hedged liability adjustments	$ (18)	$ (37)
Hedged Liability, Statement of Financial Position [Extensible Enumeration]	Deposits	Deposits
Long-term debt
Derivatives, Fair Value [Line Items]
Carrying amount of hedged liability items	$ 8,320	$ 7,913
Active hedged liability adjustments	(221)	(407)
Discontinued hedged liability adjustments	42	72
Total hedged liability adjustments	$ (179)	$ (335)
Hedged Liability, Statement of Financial Position [Extensible Enumeration]	Long-term debt (includes $7.1 billion and $7.5 billion designated under fair value option at September 30, 2024 and December 31, 2023, respectively)	Long-term debt (includes $7.1 billion and $7.5 billion designated under fair value option at September 30, 2024 and December 31, 2023, respectively)