Significant Accounting Policies - Additional Information (Detail) (USD $)	0 Months Ended		4 Months Ended	8 Months Ended	12 Months Ended
	Apr. 30, 2014	Apr. 29, 2014	Apr. 29, 2014	Dec. 31, 2014	Dec. 31, 2014 collection_bucket	Dec. 31, 2013	Dec. 31, 2012	Apr. 30, 2014
Accounting Policies [Abstract]
Beginning equity balance post-spin-off	$ 1,710,000,000							$ 1,710,000,000
Preferred stock value outstanding	565,000,000							565,000,000
Special cash contribution from Navient	473,000,000				472,718,000	0	0
Accounts, Notes, Loans and Financing Receivable [Line Items]
Private Education Loan loss confirmation period (in years)					1 year
Basis period for actual collection experience					16 months
Period of Collection Experience Using Two Hundred Twelve Day Charge Off Strategies					7 months
FFELP Loan loss confirmation period (in years)					2 years
Loan delinquent period			90 days
Number of Data Collection Buckets Used					4
Period of Collection Experience Using One Hundred Twenty Day Charge Off Strategies					9 months
Minimum days past due that company may required spin-off company to purchase loans					90 days
Period of hardship forbearance					6 months
Private education loans				8,246,647,000	8,246,647,000	6,506,642,000
Loss confirmation period	1 year	2 years
Percentage of Private Education Loans related to borrowers inschool, grace or deferment				36.00%	36.00%	39.00%
Dollar amount of change in allowance due to policy change					14,000,000
Period after last payment contractually due private education loan considered to be delinquent					31 days
Percentage reimbursement on all qualifying default claims period one				98.00%	98.00%
Percentage reimbursement on all qualifying default claims period three				100.00%	100.00%
Percentage reimbursement on all qualifying default claims period two				97.00%	97.00%
Consolidation loan rebate fee					1.05%
Loans sold			805,000,000			2,400,000,000	2,600,000,000
Gains on sales of loans, net			36,000,000	85,000,000	121,359,000	196,593,000	235,202,000
Tax indemnification receivable	291,000,000			240,311,000	240,311,000	0		291,000,000
Remaining amount of indemnification				224,000,000	224,000,000
Deferred tax asset discount	27,000,000			16,000,000	16,000,000			27,000,000
Deferred tax liability	310,000,000							310,000,000
Deferred taxes	283,000,000			252,000,000	252,000,000			283,000,000
Deferred tax assets	310,000,000							310,000,000
Deferred tax asset discount	19,000,000							19,000,000
Tax liability balance				268,000,000	268,000,000
Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan delinquent period	30 days	150 days			30 days
Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan delinquent period	120 days	212 days			120 days
FFELP Loans Rehabilitated [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans purchased					7,464,000	474,293,000
Percent of loan par value				101.67%	101.67%	95.00%
Split Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Private education loans				$ 117,000,000	$ 117,000,000