Investment Securities (Significant Unobservable Inputs) (Details) (USD $)	12 Months Ended
Dec. 31, 2014 Investment	Dec. 31, 2013
Quantitative information for Level 3 Fair Value Measurements Assets
Fair Value, Assets Measured on Recurring Basis, Transfers out	$ 97,800,000	$ 217,600,000
Number of Investments with Significant Unobseravble Inputs	1
Standard Poors NR Rating [Member] \| Redeemable preferred stocks \| Discounted cash flows
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	71,100,000	71,000,000
Standard Poors NR Rating [Member] \| Redeemable preferred stocks \| Discount Yield
Quantitative information for Level 3 Fair Value Measurements Assets
Discount Yield (as a percent)	7.10%	7.40%
Standard Poors NR Rating [Member] \| Private equity funds \| Multiple of GAAP book value
Quantitative information for Level 3 Fair Value Measurements Assets
Book Value Multiple to Calculate Fair Value	110.00%	100.00%
Assets, Fair Value Disclosure	40,200,000	35,600,000
Standard Poors NR Rating [Member] \| Private equity funds \| Recent transaction [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	20,100,000	10,500,000
Standard Poors NR Rating [Member] \| Private equity funds \| Average Share Price [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Average Share Price Used As Unobservable Input	1.06	1.10
Standard Poors NR Rating [Member] \| Private equity securities \| Recent transaction [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Average Share Price Used As Unobservable Input		0.71
Assets, Fair Value Disclosure	4,500,000	3,000,000
Standard Poors NR Rating [Member] \| Private equity securities \| Multiple of EBITDA [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Unobservable Inputs	6.00
Assets, Fair Value Disclosure	3,800,000
Standard Poors NR Rating [Member] \| Mortgage-backed and asset-backed securities \| Broker Pricing
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure		22,000,000
Standard Poors NR Rating [Member] \| Seller Priority Surplus Note [Member] \| Discounted cash flows
Quantitative information for Level 3 Fair Value Measurements Assets
Timing of Interest Payments	5 years
Discount Yield (as a percent)	9.30%
Assets, Fair Value Disclosure	44,000,000
Timing of principal payments	10 years
Standard Poors NR Rating [Member] \| Pari Passu Surplus Note [Member] \| Discounted cash flows
Quantitative information for Level 3 Fair Value Measurements Assets
Timing of Interest Payments	5 years
Discount Yield (as a percent)	13.50%
Assets, Fair Value Disclosure	21,100,000
Timing of principal payments	10 years
Level 2
Quantitative information for Level 3 Fair Value Measurements Assets
Fair Value, Assets Measured on Recurring Basis, Transfers out	0	97,200,000
Level 3 Inputs \| Fixed maturity investments
Quantitative information for Level 3 Fair Value Measurements Assets
Fair Value, Assets Measured on Recurring Basis, Transfers out	97,600,000	119,400,000
durchblicker.at [Member] \| Standard Poors NR Rating [Member] \| Private equity funds \| Recent Transaction Two [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Average Share Price Used As Unobservable Input	290.96
Assets, Fair Value Disclosure	10,400,000
BE Reinsurance [Member] \| Standard Poors NR Rating [Member] \| Private equity funds \| Recent Transaction Three [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Average Share Price Used As Unobservable Input	0.13
Assets, Fair Value Disclosure	15,800,000
Centrus [Member] \| Standard Poors NR Rating [Member] \| Mortgage-backed and asset-backed securities \| Discounted cash flows
Quantitative information for Level 3 Fair Value Measurements Assets
Unobservable Inputs	0.10
Assets, Fair Value Disclosure	$ 5,600,000
Pari Passu Surplus Note [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
basis points	2.50%
Seller Priority Surplus Note [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
basis points	2.50%

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

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=25499696&loc=d3e19207-110258

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- Definition

Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

+ 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)

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- Definition

This element represents transfers out of one of the levels in the fair value hierarchy for assets measured at fair value on a recurring basis.

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