Note 9 - Securities Sold Under Agreements to Repurchase (Detail) (USD $)	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Securities Sold under Agreements to Repurchase (in Dollars)	$ 1,150,000,000	$ 1,250,000,000	$ 1,250,000,000
Weighted Average Rate Of Securities Sold Under Agreements	3.78%
Average Rate Reduction on Modified Repurchase Agreements (in Basis Points)		1.68%
Prepaid Security Sold Under Repurchase Agreement (in Dollars)	100,000,000	150,000,000
Rate of Prepaid Security Sold Under Repurchase Agreements	4.61%	4.43%
Prepayment Penalty Security Sold Under Agreements To Repurchase (in Dollars)	5,600,000	9,400,000
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 Rate Range, Minimum	0.00%
Securities Sold Under Agreements to Repurchase Minimum [Member]
Debt Instrument, Interest Rate, Stated Percentage	1.00%
Securities Sold Under Agreements to Repurchase Maximum Initial Rate [Member]
Debt Instrument, Interest Rate, Stated Percentage	3.50%
Floating to Fixed Rate Agreements Totaling $400 Million [Member]
LIBOR Minus Hundred Basis Point	LIBOR minus 200
Callable Securities [Member]
Securities Sold under Agreements to Repurchase (in Dollars)	950,000,000
Minimum [Member] | Floating to Fixed Rate Agreements Totaling $400 Million [Member]
Debt Instrument, Interest Rate, Stated Percentage	4.78%
Minimum [Member]
Debt Instrument, Interest Rate, Stated Percentage	8.00%
Debt Instrument, Basis Spread on Variable Rate	3.25%
Maximum [Member] | Floating to Fixed Rate Agreements Totaling $400 Million [Member]
Debt Instrument, Interest Rate, Stated Percentage	5.07%
Maximum [Member]
Debt Instrument, Basis Spread on Variable Rate	3.79%
Securities Sold under Agreements to Repurchase [Member]
Line of Credit Facility, Interest Rate at Period End		3.84%
Investment Securities Pledged As Collateral (in Dollars)	1,300,000,000	1,400,000,000
Terms Modified in Current Year [Member]
Securities Sold under Agreements to Repurchase (in Dollars)		200,000,000
Floating to Fixed Rate Agreements Totaling $400 Million [Member]
Number Of Floating-To-Fixed Rate Agreements	5
Total Floating To Fixed Rate (in Dollars)	$ 300,000,000
LIBOR Minus Three Hundred and Forty Basis Points	three-month LIBOR minus 340