Debt Securities Held-to-maturity - Weighted average yield and contractual maturities of debt securities HTM - Parenthetical (Details) - Held To Maturity Debt Securities - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Schedule of Held-to-maturity Securities [Line Items]
Debt securities net unrealized loss remaining in AOCI included in book value for AFS securities transferred to HTM securities	$ 614.0	$ 658.0
Asset Not Pledged as Collateral
Schedule of Held-to-maturity Securities [Line Items]
Debt securities	69.3	67.3
Asset pledged as collateral
Schedule of Held-to-maturity Securities [Line Items]
Debt securities	$ 8,000.0	$ 8,100.0