Goodwill and Intangible Assets - Finite-lived Intangible Assets (Details) - USD ($) $ in Millions	Jun. 01, 2021	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
Finite-Lived Intangible Assets [Line Items]
Accumulated Amortization		$ 354.6	$ 326.1	$ 297.8
Policies in force
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount		256.2	256.2	256.2
Accumulated Amortization		228.7	210.4	192.2
Net Carrying Amount		27.5	45.8	64.0
Agency relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount		159.2	159.2	159.2
Accumulated Amortization		71.1	65.4	59.7
Net Carrying Amount		88.1	93.8	99.5
Software rights
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount		69.1	69.1	69.1
Accumulated Amortization		54.0	49.7	45.3
Net Carrying Amount		15.1	19.4	23.8
Trade name
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount		3.6	0.0	0.0
Accumulated Amortization		0.2	0.0	0.0
Net Carrying Amount		3.4	0.0	0.0
Protective Insurance | Trade name
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	2 years
Acquired Indefinite-lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	2 years
Finite-Lived Intangible Assets
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount		488.1	484.5	484.5
Accumulated Amortization		354.0	325.5	297.2
Net Carrying Amount		$ 134.1	$ 159.0	$ 187.3