Investment Securities - Fair Value of Hedge Funds Subject to Restrictions on Redemption Frequency (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Private equity funds
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	$ 251.2	$ 249.5
Unfunded Commitments	65.8	83.7
Hedge funds
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	144.0	111.1
Unfunded Commitments	0.0	0.0
Aerospace/Defense/Government | Private equity funds
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	144.0	152.4
Unfunded Commitments	39.9	49.3
Financial services | Private equity funds
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	104.2	93.4
Unfunded Commitments	23.7	32.0
Real estate | Private equity funds
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	3.0	3.7
Unfunded Commitments	2.2	2.4
Long/short all cap global | Hedge funds
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	110.6	51.9
Unfunded Commitments	0.0	0.0
Long/short equity financials and business services | Hedge funds
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	33.4	59.2
Unfunded Commitments	0.0	0.0
Total private equity funds and hedge funds
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	395.2	360.6
Unfunded Commitments	$ 65.8	$ 83.7