Commitments And Contingencies (Details) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended		9 Months Ended									9 Months Ended		1 Months Ended
	Oct. 31, 2010	Sep. 30, 2010	Oct. 31, 2011	Oct. 31, 2010	May 31, 2011	Jan. 31, 2011	Jul. 31, 2010	Dec. 31, 2009	Jul. 31, 2006	Oct. 31, 2011 Settlement Agreements [Member]	Jan. 31, 2011 Settlement Agreements [Member]	Oct. 31, 2011 First Condition [Member]	Oct. 31, 2011 Second Condition [Member]	Dec. 31, 2011 Settlement of Litigation [Member]
Commitments And Contingencies [Line Items]
Guarantee			$ 52.6
Forfeiture action against certain accounts									50.0
Aggregate amount to be paid under settlement agreement			165.0
Amount paid under settlement agreement			91.3				17.9	1.0
Total agreed payment in respect of anticipated opt out credit			92.5				21.5
Amount holdback in respect of anticipated opt out credit							3.6
Class action settlement fund payable in cash or stock			20.0		30.0
Issuance of shares under settlement agreement			12,462,236
Issuance of shares under settlement agreement value			82.5
Aggregate expected amount to be received from sale of securities												50.0	100.0
Additional proceeds to prepay the settlement													50.0
Cash received from sales and redemptions of auction rate securities			14.1			33.4
Amount deposited into the derivative settlement fund			60.0
Percentage of outstanding share capital			2.50%
Amount certain other defendants in the direct actions and the shareholder derivative actions have paid or agreed to pay			1.4
Legal fees and expenses of the plaintiffs	9.4
Insurance proceeds in connection with the settlements of the shareholder derivative actions and the consolidated shareholder class action		16.5
Litigation settlement										96.2	146.1
Fine paid under non-prosecution agreement			1.2
Amount paid for disgorgement and pre-judgment interest			1.6
Agreement to pay plaintiffs														9.5
Additional liability recorded				$ 4.9