Changes in and Reclassifications out of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	[1]			$ 1,931.2
Interest and other borrowing costs		$ 97.8	$ 64.1	187.5	$ 117.2
Income tax effect		(10.0)	(12.7)	(18.9)	(26.4)
Ending balance		1,947.0	1,874.8	1,947.0	1,874.8
Accumulated Gain (Loss) Net Cash Flow Hedge Parent
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		12.9	10.2	11.0	18.4
Amounts recorded in AOCL related to Unrealized gain (loss) on derivative contracts, before tax		1.8	10.9	6.6	2.3
Amounts recorded in AOCL related to Unrealized gain (loss) on derivative contracts, income tax effect		0.6	0.5	1.2	1.1
Net other comprehensive (loss) income		(0.7)	6.7	1.2	(1.5)
Ending balance		12.2	16.9	12.2	16.9
Accumulated Gain (Loss) Net Cash Flow Hedge Parent | Amounts reclassified out of AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest and other borrowing costs		(2.7)	(2.0)	(5.0)	(4.3)
Income tax effect		$ (0.4)	$ (2.7)	$ (1.6)	$ (0.6)

[1] The December 31, 2023 balance sheet has been derived from audited financial statements.