Investments - Net Investment Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Net Investment Income [Line Items]
Total net investment income	$ 445.7	$ 444.8	$ 400.9	[1]
Investment portfolio
Net Investment Income [Line Items]
Investment expenses	(13.3)	(12.1)	(10.5)
Total net investment income	344.3	339.9	297.4
Investment portfolio | Voya CML Fund
Net Investment Income [Line Items]
Total net investment income	19.2
Deposit asset on reinsurance
Net Investment Income [Line Items]
Total net investment income	101.4	104.9	103.5
Fixed maturity securities | Investment portfolio
Net Investment Income [Line Items]
Investment income	287.0	269.2	247.2
Equity securities | Investment portfolio
Net Investment Income [Line Items]
Investment income	5.2	6.5	9.0
Limited partnership interests(1) | Investment portfolio
Net Investment Income [Line Items]
Investment income	44.8	59.1	40.5
Short-term and other investments | Investment portfolio
Net Investment Income [Line Items]
Investment income	$ 20.6	$ 17.2	$ 11.2

[1] Recast for the adoption of ASU 2018-12.