13. Fair Value of Financial Instruments (Details 4) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2012
U.S. government and agency [Member]
Level 3 Assets:
Fair Value, Total assets, Balance	$ 282.8	$ 320.6
Valuation Techniques	Spread matrix
Unobservable Input	Yield
Range (Weighted Average)	1.54% - 5.21% (2.98%)
State and political subdivision [Member]
Level 3 Assets:
Fair Value, Total assets, Balance	85.7	192.9
Valuation Techniques	Discounted cash flow
Unobservable Input	Yield
Range (Weighted Average)	1.80% - 3.41% (2.71%)
Foreign government [Member]
Level 3 Assets:
Fair Value, Total assets, Balance	10.1	55.0
Valuation Techniques	Spread matrix
Unobservable Input	Yield
Range (Weighted Average)	2.11%
Corporate [Member]
Level 3 Assets:
Fair Value, Total assets, Balance	2,825.9	3,733.2
Valuation Techniques	Spread matrix
Unobservable Input	Yield
Range (Weighted Average)	1.53% - 6.86% (2.78%)
Corporate Debt Securities One [Member]
Level 3 Assets:
Fair Value, Total assets, Balance	2,825.9
Valuation Techniques	Discounted cash flow
Unobservable Input	Yield
Range (Weighted Average)	1.51% - 8.24% (3.16%)
CDO/CLO [Member]
Level 3 Assets:
Fair Value, Total assets, Balance	18.0	216.5
Valuation Techniques	Discounted cash flow
Unobservable Input	Prepayment rate
Range (Weighted Average)	20% (CLOs)
CDO/CLO [member]
Level 3 Assets:
Fair Value, Total assets, Balance	18.0
Valuation Techniques	Discounted cash flow
Unobservable Input	Default rate
Range (Weighted Average)	2.5% (CLOs)
Cdo Or Clo Debt Securities One [Member]
Level 3 Assets:
Fair Value, Total assets, Balance	18.0
Valuation Techniques	Discounted cash flow
Unobservable Input	Recovery rate
Range (Weighted Average)	65% (Loans), 35% (High yield bonds), 45% (Investment grade bonds)
Cdo Or Clo Debt Securities Two [Member]
Level 3 Assets:
Fair Value, Total assets, Balance	18.0
Valuation Techniques	Discounted cash flow
Unobservable Input	Reinvestment spread
Range (Weighted Average)	3 mo LIBOR + 400bps (CLOs)
Other asset-backed [Member]
Level 3 Assets:
Fair Value, Total assets, Balance	41.9	321.0
Valuation Techniques	Discounted cash flow
Unobservable Input	Yield
Range (Weighted Average)	2.41% - 5.38% (2.66%)
Asset Backed Securities One [Member]
Level 3 Assets:
Fair Value, Total assets, Balance	41.9
Valuation Techniques	Discounted cash flow
Unobservable Input	Prepayment rate
Range (Weighted Average)	5%
Asset Backed Securities Two [Member]
Level 3 Assets:
Fair Value, Total assets, Balance	41.9
Valuation Techniques	Discounted cash flow
Unobservable Input	Default rate
Range (Weighted Average)	2.53% for 48 mos then .33% thereafter
Asset Backed Securities Three [Member]
Level 3 Assets:
Fair Value, Total assets, Balance	41.9
Valuation Techniques	Discounted cash flow
Unobservable Input	Recovery rate
Range (Weighted Average)	10% (TRUPS)
Fair value option investments [Member]
Level 3 Assets:
Fair Value, Total assets, Balance	4.8	164.1
Valuation Techniques	Discounted cash flow
Unobservable Input	Default rate
Range (Weighted Average)	0.24%
Fair Value Option Investments One [Member]
Level 3 Assets:
Fair Value, Total assets, Balance	$ 4.8
Valuation Techniques	Discounted cash flow
Unobservable Input	Recovery rate
Range (Weighted Average)	45%