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Investment Securities (Significant Unobservable Inputs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Quantitative information for Level 3 Fair Value Measurements Assets
Fair Value, Assets Measured on Recurring Basis, Transfers out	$ 118.0	$ 41.8
Standard Poors NR Rating [Member] | Preferred stocks | Par Value [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure		$ 70.0
Standard Poors NR Rating [Member] | Preferred stocks | Discount Yield
Quantitative information for Level 3 Fair Value Measurements Assets
Unobservable Inputs		70.0
Standard Poors NR Rating [Member] | Private equity funds
Quantitative information for Level 3 Fair Value Measurements Assets
Average Share Price Used As Unobservable Input	4 years	4 years
Volatility Rate	50.00%	60.00%
Risk Free Rate	1.00%	1.15%
Standard Poors NR Rating [Member] | Private equity funds | Option pricing method [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Unobservable Inputs	0.21
Assets, Fair Value Disclosure	$ 9.3	$ 9.6
Standard Poors NR Rating [Member] | Private equity funds | Discounted cash flows
Quantitative information for Level 3 Fair Value Measurements Assets
Unobservable Inputs	0.25
Assets, Fair Value Disclosure	$ 22.1
Standard Poors NR Rating [Member] | Convertible Preferred Stock | Multiple of EBITDA [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Unobservable Inputs	6.0	6.0
Assets, Fair Value Disclosure	$ 3.6	$ 5.7
Standard Poors NR Rating [Member] | Community Reinvestment Vehicle [Member] | GAAP net equity [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Unobservable Inputs	14.3	14.3
Assets, Fair Value Disclosure	$ 14.3	$ 14.3
Standard Poors NR Rating [Member] | Seller Priority Surplus Note [Member] | Discounted cash flows
Quantitative information for Level 3 Fair Value Measurements Assets
Unobservable Inputs	0.096	0.13
Assets, Fair Value Disclosure	$ 51.1	$ 38.0
Standard Poors NR Rating [Member] | Pari Passu Surplus Note [Member] | Discounted cash flows
Quantitative information for Level 3 Fair Value Measurements Assets
Unobservable Inputs	0.15	0.224
Assets, Fair Value Disclosure	$ 20.8	$ 13.5
Level 2
Quantitative information for Level 3 Fair Value Measurements Assets
Fair Value, Assets Measured on Recurring Basis, Transfers out	0.0	0.0
Level 3 Inputs | Fixed maturity investments
Quantitative information for Level 3 Fair Value Measurements Assets
Fair Value, Assets Measured on Recurring Basis, Transfers out	$ 118.0	$ 40.6
Investment A | Standard Poors NR Rating [Member] | Private equity funds | Recent transaction [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Unobservable Inputs	1.00	1.00
Assets, Fair Value Disclosure	$ 21.0	$ 21.0
Investment B [Member] | Standard Poors NR Rating [Member] | Private equity funds | Recent transaction [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Unobservable Inputs	2.52	1.03
Assets, Fair Value Disclosure	$ 3.2	$ 33.8
Investment C [Member] | Standard Poors NR Rating [Member] | Private equity funds | Recent transaction [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Unobservable Inputs		2.52
Assets, Fair Value Disclosure		$ 3.0
Investment E | Standard Poors NR Rating [Member] | Convertible Preferred Stock | Recent transaction [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Unobservable Inputs	3.83	3.83
Assets, Fair Value Disclosure	$ 27.0	$ 27.0
Pari Passu Surplus Note [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
basis points	2.50%	2.50%
Seller Priority Surplus Note [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
basis points	2.50%	2.50%

X

- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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Description of the inputs and valuation technique(s) used to measure fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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