Investments Repurchase Agreeement, Securities Lending, VIEs (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	5 Months Ended
	Jun. 30, 2012	Oct. 29, 2012	Sep. 30, 2012	Dec. 31, 2011	Jun. 30, 2012 Securities pledged as collateral	Dec. 31, 2011 Securities pledged as collateral	Jun. 30, 2012 Cash collateral, included in Payables	Dec. 31, 2011 Cash collateral, included in Payables	Mar. 31, 2012 Variable Interest Entity, Sold Variable Interest Entity, Not Primary Beneficiary	Sep. 30, 2012 Notes Receivable
Available-for-sale Securities, Including Securities Pledged [Line Items]
Fair value of loaned securities					$ 66.1	$ 233.0
Payables under securities loan agreement, including collateral held			916.0	1,069.4			68.9	248.3
Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]
Carrying value of VIE	4.3			3.5					146.1
Gain (loss) on sale on VIE	16.9
Number of tranches for VIE sales transaction		2
Financing Receivable, Net										$ 0