Investment Securities (Significant Unobservable Inputs) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) Investment	Dec. 31, 2014 USD ($) Investment
Quantitative information for Level 3 Fair Value Measurements Assets
Fair Value, Assets Measured on Recurring Basis, Transfers out	$ 41.8	$ 53.0
Number of Investments with Significant Unobseravble Inputs | Investment	1	1
Standard Poors NR Rating [Member] | Redeemable 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] | Redeemable preferred stocks | Discounted cash flows
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure		$ 71.1
Standard Poors NR Rating [Member] | Redeemable preferred stocks | Discount Yield
Quantitative information for Level 3 Fair Value Measurements Assets
Unobservable Inputs	70.0	.07065
Standard Poors NR Rating [Member] | Private equity funds | Multiple of GAAP book value [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure		$ 39.5
Standard Poors NR Rating [Member] | Private equity funds | Recent transaction [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	$ 21.0
Standard Poors NR Rating [Member] | Private equity securities | Multiple of GAAP book value
Quantitative information for Level 3 Fair Value Measurements Assets
Unobservable Inputs		290.96
Standard Poors NR Rating [Member] | Private equity securities | Recent transaction [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	$ 5.7
Standard Poors NR Rating [Member] | Private equity securities | Multiple of EBITDA [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Unobservable Inputs	6.0	6
Assets, Fair Value Disclosure		$ 3.8
Standard Poors NR Rating [Member] | Fixed maturity investments | Discounted cash flows
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure		$ 5.3
Standard Poors NR Rating [Member] | Fixed maturity investments | Discount Yield [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Unobservable Inputs		.10
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	5 years
Unobservable Inputs	0.13
Assets, Fair Value Disclosure		$ 44.0
Timing of principal payments	10 years	10 years
Standard Poors NR Rating [Member] | Seller Priority Surplus Note [Member] | Discount Yield [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Unobservable Inputs		0.093
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
Unobservable Inputs	0.224
Assets, Fair Value Disclosure	$ 13.5	$ 21.1
Timing of principal payments	10 years	10 years
Standard Poors NR Rating [Member] | Pari Passu Surplus Note [Member] | Discount Yield [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Unobservable Inputs		0.135
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	$ 40.6	$ 52.8
Ironshore [Member] | Standard Poors NR Rating [Member] | Private equity funds | Multiple of GAAP book value
Quantitative information for Level 3 Fair Value Measurements Assets
Unobservable Inputs		1.10
PassportCard [Member] | Standard Poors NR Rating [Member] | Private equity funds | Multiple of GAAP book value
Quantitative information for Level 3 Fair Value Measurements Assets
Unobservable Inputs	1.00
Surplus Note
Quantitative information for Level 3 Fair Value Measurements Assets
RBC Score	250.00%
durchblicker.at [Member] | Standard Poors NR Rating [Member] | Private equity funds | Recent transaction [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure		$ 20.1
durchblicker.at [Member] | Standard Poors NR Rating [Member] | Private equity funds | Recent Transaction Two [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Unobservable Inputs	1.03	1.06
Assets, Fair Value Disclosure	$ 33.8
Captricity [Member] | Standard Poors NR Rating [Member] | Private equity securities | Recent transaction [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Unobservable Inputs	3.83
Assets, Fair Value Disclosure	$ 27.0
durchblicker.at [Member] | Standard Poors NR Rating [Member] | Private equity funds | Option pricing method [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	$ 9.6
durchblicker.at [Member] | Standard Poors NR Rating [Member] | Private equity funds | Recent Transaction Three [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure		$ 10.4
TaClaro [Member] | Standard Poors NR Rating [Member] | Private equity securities | Recent transaction [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Unobservable Inputs		.71
Assets, Fair Value Disclosure		$ 4.5
BE Reinsurance [Member] | 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
Volatility Rate	60.00%
Risk Free Rate	1.15%
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%