Quantitative Information Regarding Significant Unobservable Inputs (Details) - Fair Value, Inputs, Level 3 $ in Millions		Sep. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Discounted Cash Flow | Embedded Derivative in Modified Coinsurance Arrangement
Fair Value Measurement Inputs and Valuation Techniques
Embedded Derivative in Modified Coinsurance Arrangement		$ (37.5)	$ (31.1)
Embedded Derivative Liability, Measurement Input	[1]	us-gaap:ProjectedCashFlowsActuarialAssumptionsMember	us-gaap:ProjectedCashFlowsActuarialAssumptionsMember
All Other Corporate Bonds - Private | Market Approach
Fair Value Measurement Inputs and Valuation Techniques
All Other Corporate Bonds - Private		$ 120.5	$ 148.5
Debt Securities, Available-for-sale, Measurement Input	[2]	us-gaap:MarketConventionPricedatParMember	us-gaap:MarketConventionPricedatParMember
All Other Corporate Bonds - Private | Market Approach | Measurement Input, Discount for Lack of Marketability | Minimum
Fair Value Measurement Inputs and Valuation Techniques
Debt Securities, Available-for-sale, Measurement Input	[3]	0.0864	0.0025
All Other Corporate Bonds - Private | Market Approach | Measurement Input, Discount for Lack of Marketability | Maximum
Fair Value Measurement Inputs and Valuation Techniques
Debt Securities, Available-for-sale, Measurement Input	[3]	0.0864	0.0025
All Other Corporate Bonds - Private | Market Approach | Measurement Input, Discount for Lack of Marketability | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques
Debt Securities, Available-for-sale, Measurement Input	[3]	0.0864	0.0025
All Other Corporate Bonds - Private | Market Approach | Measurement Input, Entity Credit Risk | Minimum
Fair Value Measurement Inputs and Valuation Techniques
Debt Securities, Available-for-sale, Measurement Input	[4]	0.0035	0.0025
All Other Corporate Bonds - Private | Market Approach | Measurement Input, Entity Credit Risk | Maximum
Fair Value Measurement Inputs and Valuation Techniques
Debt Securities, Available-for-sale, Measurement Input	[4]	0.0050	0.1099
All Other Corporate Bonds - Private | Market Approach | Measurement Input, Entity Credit Risk | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques
Debt Securities, Available-for-sale, Measurement Input	[4]	0.0042	0.0100
Equity Securities | Market Approach
Fair Value Measurement Inputs and Valuation Techniques
Equity Securities - Private		$ 4.6	$ 4.6
Equity Securities, FV-NI, Measurement Input	[2]	us-gaap:MarketConventionPricedatCostorOwnersEquityMember	us-gaap:MarketConventionPricedatCostorOwnersEquityMember

[1] Represents various actuarial assumptions required to derive the liability cash flows including incidence, termination, and lapse rates

[2] Represents a decision to price based on par value, cost, or owner's equity when limited data is available

[3] Represents basis point adjustments to apply a discount due to the illiquidity of an investment

[4] Represents basis point adjustments for credit-specific factors