Investments - Net Investment Gains (Losses) by Transaction Type (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Investments, Debt and Equity Securities [Abstract]
Credit loss impairments	$ 0.0	$ 0.0
Intent-to-sell impairments	0.0	0.0
Total impairments	0.0	0.0
Sales and other, net	2.0	0.2
Change in fair value - equity securities	(1.3)	(1.2)
Change in fair value and gains (losses) realized on settlements - derivatives	(2.9)	(2.3)
Net investment gains (losses)	$ (2.2)	$ (3.3)