Income Taxes - Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Deferred Tax Liabilities:
Software Development	$ 419.9	$ 394.9
Depreciation and Amortization	0.0	23.9
Deferred Tax Assets, Compensation And Benefits	0.0	70.2
Compensation and Benefits	9.5	0.0
State Taxes, net	46.7	46.8
Other Liabilities	85.2	53.4
Gross Deferred Tax Liabilities	561.3	519.0
Deferred Tax Assets:
Depreciation and Amortization	38.4	0.0
Allowance for Credit Losses	43.2	46.2
Unrealized Losses on Securities, net	143.3	244.6
Tax Credit and Loss Carryforwards	157.9	121.2
Other Assets	117.2	116.0
Gross Deferred Tax Assets	500.0	598.2
Valuation Reserve	(157.9)	(121.2)
Deferred Tax Assets, net of Valuation Reserve	342.1	477.0
Net Deferred Tax Assets (Liabilities)	$ (219.2)	$ (42.0)