Investments Repurchase Agreement, Securities Lending, VIEs (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	5 Months Ended	9 Months Ended
	Jun. 30, 2012	Oct. 29, 2012	Sep. 30, 2012 Payments	Dec. 31, 2011	Sep. 30, 2012 Collateralized loan obligations Not a primary beneficiary of the VIE	Dec. 31, 2011 Collateralized loan obligations Not a primary beneficiary of the VIE	Sep. 30, 2012 Securities pledged as collateral	Dec. 31, 2011 Securities pledged as collateral	Sep. 30, 2012 Cash collateral, included in Payables	Dec. 31, 2011 Cash collateral, included in Payables	Mar. 31, 2012 Sold variable interest entity Not a primary beneficiary of the VIE	Sep. 30, 2012 Notes Receivable
Available-for-sale Securities Including Securities Pledged [Line Items]
Fair value of loaned securities							$ 149.4	$ 515.8
Payables under securities loan agreement, including collateral held			312.5	634.8					150.8	524.8
Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]
Carrying value of VIE					1.3	0.9					331.9
Gain (loss) on sale of VIE	38.7
Number of tranches for VIE sales transaction		2
Financing Receivable, Net												$ 23.0
Variable Interest Entity, Sale Transaction, Number of Installments			2