Fair Value (Schedule of Additional Information About Significant Unobservable Inputs Used in Fair Valuations of Level 3) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Fair Value [Line Items]
Fair Value	$ 60.5	$ 61.7	$ 104.2
Fixed Maturities | Municipal | Income Approach Valuation Technique | Level 3
Fair Value [Line Items]
Fair Value	$ 34.4	$ 25.7
Fixed Maturities | Municipal | Discount For Small Issue Size | Income Approach Valuation Technique | Level 3 | Minimum [Member]
Fair Value [Line Items]
Range (Weighted Average)	0.60%	0.60%
Fixed Maturities | Municipal | Discount For Small Issue Size | Income Approach Valuation Technique | Level 3 | Maximum [Member]
Fair Value [Line Items]
Range (Weighted Average)	6.80%	4.50%
Fixed Maturities | Municipal | Discount For Small Issue Size | Income Approach Valuation Technique | Level 3 | Weighted Average [Member]
Fair Value [Line Items]
Range (Weighted Average)	3.20%	2.00%
Fixed Maturities | Municipal | Discount For Above Market Coupon | Income Approach Valuation Technique | Level 3 | Minimum [Member]
Fair Value [Line Items]
Range (Weighted Average)	0.30%	0.30%
Fixed Maturities | Municipal | Discount For Above Market Coupon | Income Approach Valuation Technique | Level 3 | Maximum [Member]
Fair Value [Line Items]
Range (Weighted Average)	1.00%	1.00%
Fixed Maturities | Municipal | Discount For Above Market Coupon | Income Approach Valuation Technique | Level 3 | Weighted Average [Member]
Fair Value [Line Items]
Range (Weighted Average)	0.40%	0.40%
Fixed Maturities | Municipal | Discount For Credit Stress | Income Approach Valuation Technique | Level 3 | Minimum [Member]
Fair Value [Line Items]
Range (Weighted Average)	0.90%
Fixed Maturities | Municipal | Discount For Credit Stress | Income Approach Valuation Technique | Level 3 | Maximum [Member]
Fair Value [Line Items]
Range (Weighted Average)	1.50%
Fixed Maturities | Municipal | Discount For Credit Stress | Income Approach Valuation Technique | Level 3 | Weighted Average [Member]
Fair Value [Line Items]
Range (Weighted Average)	1.20%
Fixed Maturities | Corporate | Income Approach Valuation Technique | Level 3
Fair Value [Line Items]
Fair Value	$ 3.7	$ 9.4
Fixed Maturities | Corporate | Discount For Small Issue Size | Income Approach Valuation Technique | Level 3
Fair Value [Line Items]
Range (Weighted Average)	1.00%
Fixed Maturities | Corporate | Discount For Small Issue Size | Income Approach Valuation Technique | Level 3 | Minimum [Member]
Fair Value [Line Items]
Range (Weighted Average)		0.50%
Fixed Maturities | Corporate | Discount For Small Issue Size | Income Approach Valuation Technique | Level 3 | Maximum [Member]
Fair Value [Line Items]
Range (Weighted Average)		1.00%
Fixed Maturities | Corporate | Discount For Small Issue Size | Income Approach Valuation Technique | Level 3 | Weighted Average [Member]
Fair Value [Line Items]
Range (Weighted Average)	1.00%	0.70%
Fixed Maturities | Corporate | Discount For Above Market Coupon | Income Approach Valuation Technique | Level 3 | Minimum [Member]
Fair Value [Line Items]
Range (Weighted Average)	0.30%	0.30%
Fixed Maturities | Corporate | Discount For Above Market Coupon | Income Approach Valuation Technique | Level 3 | Maximum [Member]
Fair Value [Line Items]
Range (Weighted Average)	0.80%	0.80%
Fixed Maturities | Corporate | Discount For Above Market Coupon | Income Approach Valuation Technique | Level 3 | Weighted Average [Member]
Fair Value [Line Items]
Range (Weighted Average)	0.60%	0.60%
Fixed Maturities | Corporate | Discount For Credit Stress | Income Approach Valuation Technique | Level 3
Fair Value [Line Items]
Range (Weighted Average)	10.00%
Fixed Maturities | Corporate | Discount For Credit Stress | Income Approach Valuation Technique | Level 3 | Weighted Average [Member]
Fair Value [Line Items]
Range (Weighted Average)	10.00%
Fixed Maturities | Commercial mortgage-backed | Income Approach Valuation Technique | Level 3
Fair Value [Line Items]
Fair Value	$ 17.0	$ 21.4
Fixed Maturities | Commercial mortgage-backed | Discount For Small Issue Size | Income Approach Valuation Technique | Level 3
Fair Value [Line Items]
Range (Weighted Average)		0.50%
Fixed Maturities | Commercial mortgage-backed | Discount For Small Issue Size | Income Approach Valuation Technique | Level 3 | Minimum [Member]
Fair Value [Line Items]
Range (Weighted Average)	0.50%
Fixed Maturities | Commercial mortgage-backed | Discount For Small Issue Size | Income Approach Valuation Technique | Level 3 | Maximum [Member]
Fair Value [Line Items]
Range (Weighted Average)	1.00%
Fixed Maturities | Commercial mortgage-backed | Discount For Small Issue Size | Income Approach Valuation Technique | Level 3 | Weighted Average [Member]
Fair Value [Line Items]
Range (Weighted Average)	0.50%	0.50%
Fixed Maturities | Commercial mortgage-backed | Discount For Above Market Coupon | Income Approach Valuation Technique | Level 3
Fair Value [Line Items]
Range (Weighted Average)	0.50%
Fixed Maturities | Commercial mortgage-backed | Discount For Above Market Coupon | Income Approach Valuation Technique | Level 3 | Minimum [Member]
Fair Value [Line Items]
Range (Weighted Average)		0.50%
Fixed Maturities | Commercial mortgage-backed | Discount For Above Market Coupon | Income Approach Valuation Technique | Level 3 | Maximum [Member]
Fair Value [Line Items]
Range (Weighted Average)		0.80%
Fixed Maturities | Commercial mortgage-backed | Discount For Above Market Coupon | Income Approach Valuation Technique | Level 3 | Weighted Average [Member]
Fair Value [Line Items]
Range (Weighted Average)	0.50%	0.50%
Fixed Maturities | Commercial mortgage-backed | Discount For Credit Stress | Income Approach Valuation Technique | Level 3
Fair Value [Line Items]
Range (Weighted Average)		0.50%
Fixed Maturities | Commercial mortgage-backed | Discount For Credit Stress | Income Approach Valuation Technique | Level 3 | Weighted Average [Member]
Fair Value [Line Items]
Range (Weighted Average)		0.50%
Fixed Maturities | Commercial mortgage-backed | Discount For Lease Structure | Income Approach Valuation Technique | Level 3
Fair Value [Line Items]
Range (Weighted Average)	0.30%	0.30%
Fixed Maturities | Commercial mortgage-backed | Discount For Lease Structure | Income Approach Valuation Technique | Level 3 | Weighted Average [Member]
Fair Value [Line Items]
Range (Weighted Average)	0.30%	0.30%
Fixed Maturities | Asset-backed | Income Approach Valuation Technique | Level 3
Fair Value [Line Items]
Fair Value	$ 0.5
Fixed Maturities | Asset-backed | Discount For Small Issue Size | Income Approach Valuation Technique | Level 3
Fair Value [Line Items]
Range (Weighted Average)	0.70%
Fixed Maturities | Asset-backed | Discount For Small Issue Size | Income Approach Valuation Technique | Level 3 | Weighted Average [Member]
Fair Value [Line Items]
Range (Weighted Average)	0.70%
Equity Securities | Net Tangible Asset Market Multiples | Market comparables [Member] | Level 3
Fair Value [Line Items]
Fair Value	$ 1.1	$ 1.1
Fair value measurement market multiples	1.0	1.0
Equity Securities | Net Tangible Asset Market Multiples | Market comparables [Member] | Level 3 | Weighted Average [Member]
Fair Value [Line Items]
Fair value measurement market multiples	1.0	1.0
Other securities | Income Approach Valuation Technique | Level 3
Fair Value [Line Items]
Fair Value	$ 3.6	$ 3.8
Other securities | Discount Rate [Member] | Income Approach Valuation Technique | Level 3
Fair Value [Line Items]
Range (Weighted Average)	18.00%	18.00%
Other securities | Discount Rate [Member] | Income Approach Valuation Technique | Level 3 | Weighted Average [Member]
Fair Value [Line Items]
Range (Weighted Average)	18.00%	18.00%