Equity Securities (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Schedule Of Investments [Line Items]
Realized and unrealized net gains (losses) on equity securities	$ (12.2)	$ 37.5	$ (1.3)	$ 49.9
Net unrealized gains (losses) on equity securities	(13.2)	39.5	(2.7)	51.2
Common Stock | Offerpad Inc [Member]
Schedule Of Investments [Line Items]
Net unrealized gains (losses) on equity securities	$ (18.8)	$ 25.9	$ (29.8)	$ 26.5