Allowance for Loan Losses - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Jul. 01, 2006
Receivables [Abstract]
Troubled Debt Restructuring	$ 13.1
Criteria for loans to be considered as nonperforming	90 days
Tier One of Government Guarantee	97.00%		97.00%
Ffelp Loans Net	$ 832
Percentage of FFELP Rehabilitation Loans	62.50%	62.90%
Period of loans past due that have accrued interest	90 days