Allowance for Loan Losses - Additional Information (Detail) - USD ($) $ in Millions		12 Months Ended
	Apr. 29, 2014	Dec. 31, 2015	Dec. 31, 2014	Jul. 01, 2006
Schedule Of Allowance For Credit Losses And Recorded Investment In Financing Receivables Table [Line Items]
Period of loans delinquent sold to subsidiary	90 days
Period after grace period for forbearance allowance for loans		9 months
Forbearance period after grace period for loans		6 months
Period of forbearance period to be classified as TDR		3 months
Percentage of loans granted forbearance		23.00%	10.00%
Criteria for loans to be considered as nonperforming		90 days
Tier 1 of government guarantee				97.00%
TDR payment default period		60 days
Period of loans past due that have accrued interest		90 days
FFELP Loans
Schedule Of Allowance For Credit Losses And Recorded Investment In Financing Receivables Table [Line Items]
Tier 1 of government guarantee		97.00%
Private Education Loans
Schedule Of Allowance For Credit Losses And Recorded Investment In Financing Receivables Table [Line Items]
Troubled debt restructuring		$ 307.2