Goodwill and Intangible Assets - Finite-lived Intangible Assets (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Finite-Lived Intangible Assets [Line Items]
Accumulated Amortization	$ 283.6	$ 247.7	$ 211.7
Policies in force
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	256.2	256.2	256.2
Accumulated Amortization	155.6	137.3	119.0
Net Carrying Amount	100.6	118.9	137.2
Agency relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	159.2	159.2	159.2
Accumulated Amortization	48.3	42.6	37.0
Net Carrying Amount	110.9	116.6	122.2
Software rights
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	79.1	79.1	79.1
Accumulated Amortization	45.4	40.1	34.7
Net Carrying Amount	33.7	39.0	44.4
Trade name
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	34.8	34.8	34.8
Accumulated Amortization	33.7	27.1	20.4
Net Carrying Amount	1.1	7.7	14.4
Finite-Lived Intangible Assets
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	529.3	529.3	529.3
Accumulated Amortization	283.0	247.1	211.1
Net Carrying Amount	$ 246.3	$ 282.2	$ 318.2