Investment Securities - Fair Value of Hedge Funds Subject to Restrictions on Redemption Frequency (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Private equity funds
Investment securities
Fair Value	$ 249.5	$ 248.6
Unfunded Commitments	83.7	57.7
Hedge funds
Investment securities
Fair Value	111.2	64.3
Unfunded Commitments	0.0	0.0
Aerospace/Defense/Government | Private equity funds
Investment securities
Fair Value	152.4	157.2
Unfunded Commitments	49.3	17.4
Financial services | Private equity funds
Investment securities
Fair Value	93.4	87.5
Unfunded Commitments	32.0	37.8
Real estate | Private equity funds
Investment securities
Fair Value	3.7	3.9
Unfunded Commitments	2.4	2.5
Long/short equity financials and business services | Hedge funds
Investment securities
Fair Value	59.2	54.4
Unfunded Commitments	0.0	0.0
Long/short all cap global | Hedge funds
Investment securities
Fair Value	52.0	0.0
Unfunded Commitments	0.0	0.0
European small/mid cap | Hedge funds
Investment securities
Fair Value	0.0	9.9
Unfunded Commitments	0.0	0.0
Private equity funds and hedge funds
Investment securities
Fair Value	360.7	312.9
Unfunded Commitments	$ 83.7	$ 57.7