Investments - Net Realized Gains on Sales of Investments (Details) - Fixed Maturities - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Net Investment Income [Line Items]
Gains on Sales	$ 1.9	$ 5.9	$ 39.7	$ 11.2
Losses on Sales	$ (0.3)	$ (2.5)	$ (4.8)	$ (6.5)

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration