LOAN PORTFOLIO - Corporation's Aging of Loans Held for Investment Portfolio (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 numberofpayments	Dec. 31, 2013 numberofpayments
Accounts Notes And Loans Receivable [Line Items]
Loans considered to be defaulted if borrower has failed to make payment for a period or more than the period	0 years 2 months 29 days	0 years 2 months 29 days
Period during which credit card loans continue to accrue finance charges and fees	0 years 5 months 27 days	0 years 5 months 27 days
Defaulted loans collateralizing Ginnie Mae (GNMA) securities	$ 9.3	$ 11.5
Minimum Number of Payments in Arrears to Consider Commercial Mortgage and Construction Loan as Past Due	2	2
Residential mortgage loans insured by FHA or guaranteed by the VA	40.4	37.0
Period of residential mortgage loan that are no longer accruing interest	1 year 6 months 0 days	1 year 6 months 0 days
Fha Va And Other Government Guaranteed Loans [Member]
Accounts Notes And Loans Receivable [Line Items]
30-59 Days past due Mortgages	14.0	23.9
Residential Mortgage [Member]
Accounts Notes And Loans Receivable [Line Items]
30-59 Days past due Mortgages	189.1	166.7
Commercial Mortgage [Member]
Accounts Notes And Loans Receivable [Line Items]
30-59 Days past due Mortgages	20.8	18.4
Residential Construction [Member]
Accounts Notes And Loans Receivable [Line Items]
30-59 Days past due Mortgages	1.0	2.5
Land Construction [Member]
Accounts Notes And Loans Receivable [Line Items]
30-59 Days past due Mortgages	$ 0.8	$ 0.9