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	Sep. 30, 2023	Dec. 31, 2022
Asset pledged as collateral
Schedule of Available-for-sale Securities [Line Items]
Debt securities	$ 12.9	$ 11.3
Debt securities served as collateral for public funds	12.0	10.3
Asset Not Pledged as Collateral
Schedule of Available-for-sale Securities [Line Items]
Debt securities	$ 4.2	$ 6.4