Unrecognized tax benefits (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Income Tax [Abstract]
Balance at Beginning of Year	$ 136.0	$ 156.7	$ 177.4
Decreases for Tax Positions Related to Prior Years	(20.7)	(20.7)	(20.7)
Balance at End of Year	115.3	136.0	156.7
Less Tax Attributable to Temporary Items Included Above	0.0	(21.2)	(42.4)
Total Unrecognized Tax Benefits that if Recognized Would Affect the Effective Tax Rate	$ 115.3	$ 114.8	$ 114.3