Income Taxes - Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Deferred Tax Liabilities:
Software Development	$ 394.9	$ 354.7
Depreciation and Amortization	23.9	122.6
Deferred Tax Assets, Compensation And Benefits	70.2	0.0
Compensation and Benefits	0.0	5.2
State Taxes, net	46.8	58.3
Other Liabilities	53.4	42.1
Gross Deferred Tax Liabilities	519.0	582.9
Deferred Tax Assets:
Allowance for Credit Losses	46.2	41.8
Unrealized Losses on Securities, net	244.6	427.3
Tax Credit and Loss Carryforwards	121.2	95.3
Other Assets	116.0	143.7
Gross Deferred Tax Assets	598.2	708.1
Valuation Reserve	(121.2)	(95.3)
Deferred Tax Assets, net of Valuation Reserve	477.0	612.8
Net Deferred Tax Assets (Liabilities)	$ (42.0)
Net Deferred Tax Assets (Liabilities)		$ 29.9