Investment Securities (Significant Unobservable Inputs) (Details) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 input
Standard & Poor's, AAA Rating | Non-Agency Residential Mortgage [Member] | Broker Pricing [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	$ 58.3
Fair Value Measurements, Valuation Techniques	102.56
NR | Private equity funds | Discounted cash flows
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	$ 22.1	$ 22.1
Fair Value Measurements, Valuation Techniques	0.25	0.25
NR | Private equity funds | Option pricing method [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	$ 9.4	$ 9.3
Fair Value Measurements, Valuation Techniques	0.21	0.21
NR | Convertible Preferred Stock | Multiple of EBITA [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	$ 3.7	$ 3.6
Unobservable Inputs | input			0
Fair Value Measurements, Valuation Techniques	6	6.0
NR | Community Reinvestment Vehicle [Member] | GAAP net equity [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	$ 14.5	$ 14.3
Fair Value Measurements, Valuation Techniques	14.5	14.3
NR | Seller Priority Surplus Note [Member] | Discounted cash flows
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	$ 48.1	$ 51.1
Fair Value Measurements, Valuation Techniques	0.106	0.096
NR | Pari Passu Surplus Note [Member] | Discounted cash flows
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	$ 21.5	$ 20.8
Fair Value Measurements, Valuation Techniques	0.150	0.15
Investment A [Member] | NR | Private equity funds | Recent transaction [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	$ 21.0	$ 21.0
Fair Value Measurements, Valuation Techniques	1	1.00
Investment B [Member] | NR | Private equity funds | Recent transaction [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	$ 3.4	$ 3.2
Fair Value Measurements, Valuation Techniques	2.521	2.52
Investment E [Member] | NR | Convertible Preferred Stock | Recent transaction [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	$ 27.0	$ 27.0
Fair Value Measurements, Valuation Techniques	3.83	3.83
Investment C | NR | Private equity funds
Quantitative information for Level 3 Fair Value Measurements Assets
Time Until Expiration of Security	4 years	4 years
Volatility Rate	50.00%	50.00%
Risk Free Rate	1.00%	1.00%
Standard & Poor's, B Rating [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Basis points	4.00%	2.50%
Standard & Poor's, CCC Rating [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Basis points	4.00%	2.50%