Goodwill and Intangible Assets - Schedule of Definite and Indefinite Life Intangible Assets (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	$ 706.4	$ 607.5
Indefinite-lived Intangible Assets (Excluding Goodwill)	50.3	47.8
Intangible Assets, Gross (Excluding Goodwill), Total	756.7	655.3
Finite-Lived Intangible Assets, Accumulated Amortization	413.5	335.2
Finite-Lived Intangible Assets, Net	292.9	272.3
Intangible Assets, Net (Including Goodwill)	343.2	320.1
Trade Names
Finite-Lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets (Excluding Goodwill)	5.2	5.2
Insurance Licenses
Finite-Lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets (Excluding Goodwill)	45.1	42.6
Value of Business Acquired
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	237.5	194.5
Finite-Lived Intangible Assets, Accumulated Amortization	218.5	174.2
Finite-Lived Intangible Assets, Net	19.0	20.3
Customer Relationships
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	43.8	39.0
Finite-Lived Intangible Assets, Accumulated Amortization	38.1	35.6
Finite-Lived Intangible Assets, Net	5.7	3.4
Agent Relationships
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	81.6	74.4
Finite-Lived Intangible Assets, Accumulated Amortization	23.6	16.8
Finite-Lived Intangible Assets, Net	58.0	57.6
Trade Names
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	1.8
Finite-Lived Intangible Assets, Accumulated Amortization	0.9
Finite-Lived Intangible Assets, Net	0.9
Internal Use Software
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	341.7	299.6
Finite-Lived Intangible Assets, Accumulated Amortization	132.4	108.6
Finite-Lived Intangible Assets, Net	$ 209.3	$ 191.0