Goodwill and Intangible Assets - Finite-lived Intangible Assets (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Finite-Lived Intangible Assets [Line Items]
Accumulated Amortization	$ 299.4	$ 247.7	$ 229.7
Policies in force
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	256.2	256.2	256.2
Accumulated Amortization	164.7	137.3	128.1
Net Carrying Amount	91.5	118.9	128.1
Agency relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	159.2	159.2	159.2
Accumulated Amortization	51.2	42.6	39.8
Net Carrying Amount	108.0	116.6	119.4
Software rights
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	79.1	79.1	79.1
Accumulated Amortization	48.1	40.1	37.4
Net Carrying Amount	31.0	39.0	41.7
Trade name
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	34.8	34.8	34.8
Accumulated Amortization	34.8	27.1	23.8
Net Carrying Amount	0.0	7.7	11.0
Finite-Lived Intangible Assets
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	529.3	529.3	529.3
Accumulated Amortization	298.8	247.1	229.1
Net Carrying Amount	$ 230.5	$ 282.2	$ 300.2