Debt Securities Available for Sale - Weighted average yield and contractual maturities of debt securities AFS - Parenthetical (Details) - Debt securities available-for-sale - USD ($) $ in Billions	Mar. 31, 2024	Dec. 31, 2023
Asset pledged as collateral
Schedule of Available-for-sale Securities [Line Items]
Debt securities	$ 11.8	$ 12.0
Debt securities served as collateral for public funds	11.0	11.1
Asset Not Pledged as Collateral
Schedule of Available-for-sale Securities [Line Items]
Debt securities	$ 6.2	$ 4.6