Goodwill and Intangible Assets - Schedule of Definite and Indefinite Life Intangible Assets (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Definite Life Intangibles, Gross Carrying Amount	$ 607.5	$ 569.5
Definite Life Intangibles, Accumulated Amortization	335.2	288.9
Definite Life Intangibles, Net Amount	272.3	280.6
Indefinite Life Intangible Assets	47.8	47.8
Total Intangible Assets, Gross Carrying Amount	655.3	617.3
Total Intangible Assets, Net Amount	320.1	328.4
Trade Names
Finite-Lived Intangible Assets [Line Items]
Indefinite Life Intangible Assets	5.2	5.2
Insurance Licenses
Finite-Lived Intangible Assets [Line Items]
Indefinite Life Intangible Assets	42.6	42.6
Value of Business Acquired
Finite-Lived Intangible Assets [Line Items]
Definite Life Intangibles, Gross Carrying Amount	194.5	194.5
Definite Life Intangibles, Accumulated Amortization	174.2	170.4
Definite Life Intangibles, Net Amount	20.3	24.1
Customer Relationships
Finite-Lived Intangible Assets [Line Items]
Definite Life Intangibles, Gross Carrying Amount	39.0	39.0
Definite Life Intangibles, Accumulated Amortization	35.6	34.7
Definite Life Intangibles, Net Amount	3.4	4.3
Agent Relationships
Finite-Lived Intangible Assets [Line Items]
Definite Life Intangibles, Gross Carrying Amount	74.4	74.4
Definite Life Intangibles, Accumulated Amortization	16.8	11.9
Definite Life Intangibles, Net Amount	57.6	62.5
Internal-Use Software
Finite-Lived Intangible Assets [Line Items]
Definite Life Intangibles, Gross Carrying Amount	299.6	261.6
Definite Life Intangibles, Accumulated Amortization	108.6	71.9
Definite Life Intangibles, Net Amount	$ 191.0	$ 189.7