Note 9 - Securities Sold Under Agreements to Repurchase (Detail) (USD $)	Mar. 31, 2012	Dec. 31, 2011	May 31, 2011	May 31, 2011 Securities Sold Under Agreements to Repurchase Minimum [Member]	May 31, 2018 Securities Sold Under Agreements to Repurchase Maximum Initial Rate [Member]	May 31, 2011 Securities Sold Under Agreements to Repurchase Maximum Initial Rate [Member]	May 31, 2018 Securities Sold Under Agreements to Repurchase Minimum Interest Rate [Member]	May 31, 2018 Minimum [Member]	May 31, 2011 Minimum [Member]	May 31, 2018 Maximum [Member]	May 31, 2011 Maximum [Member]
Securities Sold under Agreements to Repurchase (in Dollars)	$ 1,400,000,000	$ 1,400,000,000
Weighted Average Rate Of Securities Sold Under Agreements	4.14%	4.14%
Prepaid Security Sold Under Repurchase Agreement (in Dollars)			50,000,000
Rate of Prepaid Security Sold Under Repurchase Agreements			4.83%
Prepayment Penalty Security Sold Under Agreements To Repurchase (in Dollars)			1,700,000
Number Of Floating-To-Fixed Rate Agreements	14
Total Floating To Fixed Rate (in Dollars)	750,000,000
Initial Floating Rate Period On Floating-To-Fixed Rate Agreements, Months	6
Initial Floating Rate Period On Floating-To-Fixed Rate Agreements Years	1
LIBOR Minus Hundred Basis Point			LIBOR minus 100
LIBOR Minus Three Hundred and Forty Basis Points			LIBOR minus 340
Current Lowest Rate Long Term Initial Floating To Fix Security Sold Under Agreements To Repurchase									4.29%		5.07%
Number Of Fixed-To-Floating Security Sold Under Agreements To Repurchase			13
Total Fixed To Floating Rate Agreements (in Dollars)			650,000,000
Debt Instrument, Interest Rate, Stated Percentage				1.00%	8.00%	3.50%
Initial Fixed Rate Period									6		18
Remainder Of Long Term Securities			7
Debt Instrument, Basis Spread on Variable Rate								3.25%		3.75%
Long-term Debt, Weighted Average Interest Rate							0.00%
Pledged Mortgage Backed Securities for Securities Sold Under Agreements to Repurchase (in Dollars)	$ 1,500,000,000	$ 1,600,000,000