XML 68 R49.htm IDEA: XBRL DOCUMENT
v3.10.0.1

Significant Accounting Policies - Additional Information (Detail) |  | 3 Months Ended | 4 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | ---
Jul. 01, 2018 USD ($) | Dec. 31, 2018 USD ($) | Sep. 30, 2018 USD ($) | Jun. 30, 2018 USD ($) | Mar. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | Sep. 30, 2017 USD ($) | Jun. 30, 2017 USD ($) | Mar. 31, 2017 USD ($) | Apr. 29, 2014 | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Apr. 30, 2014 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Discrete tax expense |  |  |  |  |  |  |  |  |  |  |  | $ 15 |  |
Private Education Loan loss confirmation period (in years) |  |  |  |  |  |  |  |  |  |  | 1 year |  |  |
FFELP loan loss confirmation period (in years) |  |  |  |  |  |  |  |  |  |  | 2 years |  |  |
Loan delinquent period |  |  |  |  |  |  |  |  |  | 90 days |  |  |  |
Personal loans held at end of year |  | $ 1,100,000,000 |  |  |  | $ 393,700,000 |  |  |  |  | $ 1,100,000,000 | $ 393,700,000 |  |
Interest rate reduction and forbearance usage (greater than) |  |  |  |  |  |  |  |  |  |  | 3 months |  |  |
Loans And Leases Receivable, Temporary Interest Rate Reduction, Financial Difficulty Status |  | 2.00% |  |  |  |  |  |  |  |  | 2.00% |  |  |
Period of forbearance period to be classified as TDR |  |  |  |  |  |  |  |  |  |  | 3 months |  |  |
Period of forbearance |  |  |  |  |  |  |  |  |  |  | 24 months |  |  |
Period after grace period for forbearance allowance for loans |  |  |  |  |  |  |  |  |  |  | 9 months |  |  |
Forbearance period after grace period for loans |  |  |  |  |  |  |  |  |  |  | 6 months |  |  |
Percentage of loans granted forbearance (as a percentage) |  | 57.00% |  |  |  | 66.00% |  |  |  |  | 57.00% | 66.00% |  |
Percentage of Private Education Loans related to borrowers inschool, grace or deferment (as a percentage) |  | 26.00% |  |  |  | 27.00% |  |  |  |  | 26.00% | 27.00% |  |
Period after last payment contractually due private education loan considered to be delinquent |  |  |  |  |  |  |  |  |  |  | 31 days |  |  |
Percentage reimbursement on all qualifying default claims period two (as a percentage) |  | 97.00% |  |  |  |  |  |  |  |  | 97.00% |  |  |
Percentage reimbursement on all qualifying default claims period one (as a percentage) |  | 98.00% |  |  |  |  |  |  |  |  | 98.00% |  |  |
Percentage reimbursement on all qualifying default claims period three (as a percentage) |  | 100.00% |  |  |  |  |  |  |  |  | 100.00% |  |  |
Period of loss emergence to estimate credit losses incurred |  |  |  |  |  |  |  |  |  |  | 2 years |  |  |
Period of notification for withdrawal of deposits (less than or equal to) |  |  |  |  |  |  |  |  |  |  | 7 days |  |  |
Constant prepayment rate for Private Education Loans (in percentage) |  |  |  |  |  |  |  |  |  |  | 6.83% | 5.94% |  |
Variable rate |  | 1.05 |  |  |  |  |  |  |  |  | 1.05 |  |  |
Gains on sales of loans, net |  |  |  |  |  |  |  |  |  |  | $ 2,060,000 | $ 0 | $ 230,000 |
Asset balance related to securitization trust (as a percentage) |  |  |  |  |  |  |  |  |  |  | 10.00% |  |  |
Total amount of notional derivative contracts |  | $ 6,000,000,000 |  |  |  |  |  |  |  |  | $ 6,000,000,000 |  |  |
Income tax expense |  | 44,449,000 | $ (53,667,000) | $ 40,074,000 | $ 40,997,000 | $ 66,190,000 | $ 40,617,000 | $ 44,713,000 | $ 51,011,000 |  | 71,853,000 | 202,531,000 | 164,109,000 |
Income taxes receivable, net |  | 41,570,000 |  |  |  | 0 |  |  |  |  | 41,570,000 | 0 |  |
Net positive exposure |  | 27,000,000 |  |  |  | 20,000,000 |  |  |  |  | 27,000,000 | 20,000,000 |  |
Reclassification resulting from the adoption of ASU No. 2017-12 |  |  |  |  |  | (165,000) |  |  |  |  |  | (165,000) |  |
Losses on derivatives and hedging activities, net |  |  |  |  |  |  |  |  |  |  | $ 87,000 | 8,266,000 | $ 958,000 |
Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loan delinquent period |  |  |  |  |  |  |  |  |  |  | 120 days |  |  |
Split Loans |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Private education loans |  | 43,000,000 |  |  |  |  |  |  |  |  | $ 43,000,000 |  |  |
Net gain |  |  |  |  |  |  |  |  |  |  | 2,000,000 |  |  |
Navient |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred tax asset discount |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 27,000,000
Deferred tax liability |  | 24,000,000 |  |  |  |  |  |  |  |  | 24,000,000 |  |  | 310,000,000
Deferred taxes |  |  |  |  |  |  |  |  |  |  |  |  |  | 283,000,000
Income taxes receivable, net |  |  |  |  |  | 24,000,000 |  |  |  |  |  | 24,000,000 |  | 291,000,000
Deferred tax assets |  |  |  |  |  |  |  |  |  |  |  |  |  | 310,000,000
Deferred tax asset discount |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 19,000,000
CME |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total amount of notional derivative contracts |  | 5,400,000,000 |  |  |  |  |  |  |  |  | $ 5,400,000,000 |  |  |
Percent of total notional derivative contracts |  |  |  |  |  |  |  |  |  |  | 90.20% |  |  |
Amount of variation margin included as settlement |  |  |  |  |  |  |  |  |  |  | $ (16,700,000) |  |  |
LCH |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total amount of notional derivative contracts |  | 600,000,000 |  |  |  |  |  |  |  |  | $ 600,000,000 |  |  |
Percent of total notional derivative contracts |  |  |  |  |  |  |  |  |  |  | 9.80% |  |  |
Amount of variation margin included as settlement |  |  |  |  |  |  |  |  |  |  | $ (6,100,000) |  |  |
Retained Earnings |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reclassification resulting from the adoption of ASU No. 2017-12 |  |  |  |  |  | $ 264,000 |  |  |  |  |  | $ 264,000 |  |
Accumulated Other Comprehensive Income (Loss) |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reclassification resulting from the adoption of ASU No. 2018-02 |  |  |  |  | $ 600,000 |  |  |  |  |  | 592,000 |  |  |
Discontinued Operations, Disposed of by Sale |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Principal Amount Outstanding of Loans Held-in-portfolio |  |  |  | 43,000,000 |  |  |  |  |  |  |  |  |  |
Gains on sales of loans, net |  |  |  | $ 2,000,000 |  |  |  |  |  |  |  |  |  |
Accounting Standards Update 2017-12 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reclassification resulting from the adoption of ASU No. 2017-12 |  | (861,000) |  |  |  |  |  |  |  |  | (861,000) |  |  |
Accounting Standards Update 2017-12 [Member] | Retained Earnings |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reclassification resulting from the adoption of ASU No. 2017-12 |  | (591,000) |  |  |  |  |  |  |  |  | (591,000) |  |  |
Accounting Standards Update 2017-12 [Member] | Accumulated Other Comprehensive Income (Loss) |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reclassification resulting from the adoption of ASU No. 2017-12 |  | $ (270,000) |  |  |  |  |  |  |  |  | $ (270,000) |  |  |
Fair Value | Accounting Standards Update 2017-12 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net positive exposure | $ 2,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Losses on derivatives and hedging activities, net | 3,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Fair Value | Accounting Standards Update 2017-12 [Member] | Retained Earnings |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reclassification resulting from the adoption of ASU No. 2017-12 | (800,000) |  |  |  |  |  |  |  |  |  |  |  |  |
Cash Flow | Accounting Standards Update 2017-12 [Member] | Retained Earnings |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reclassification resulting from the adoption of ASU No. 2017-12 | 200,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Cash Flow | Accounting Standards Update 2017-12 [Member] | Accumulated Other Comprehensive Income (Loss) |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reclassification resulting from the adoption of ASU No. 2017-12 | $ (300,000) |  |  |  |  |  |  |  |  |  |  |  |  |
Accounting Standards Update 2016-09 | Adjustments for New Accounting Pronouncement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income tax expense |  |  |  |  |  |  |  |  | 8,500,000 |  |  |  |  |
Reclassification resulting from the adoption of ASU No. 2017-12 |  |  |  |  |  |  |  |  | $ (200,000) |  |  |  |  |

X
- Definition Aggregate notional amount specified by the derivative(s). Expressed as an absolute value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
Name: | invest_DerivativeNotionalAmount
Namespace Prefix: | invest_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | instant

X
- Definition Amount Of Variation Margin Included As Settlement + References No definition available. + Details
Name: | slm_AmountOfVariationMarginIncludedAsSettlement
Namespace Prefix: | slm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Constant Prepayment Fee, Variable Rate + References No definition available. + Details
Name: | slm_ConstantPrepaymentFeeVariableRate
Namespace Prefix: | slm_
Data Type: | xbrli:pureItemType
Balance Type: | na
Period Type: | instant

X
- Definition Constant Prepayment Rate, Private Education Loans, Percent + References No definition available. + Details
Name: | slm_ConstantPrepaymentRatePrivateEducationLoansPercent
Namespace Prefix: | slm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Deferred tax asset discount + References No definition available. + Details
Name: | slm_DeferredTaxAssetDiscount
Namespace Prefix: | slm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Deferred Tax Liabilities, Net and Liability Due to Uncertain Tax Positions + References No definition available. + Details
Name: | slm_DeferredTaxLiabilitiesNetandLiabilityDuetoUncertainTaxPositions
Namespace Prefix: | slm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Deposits, Period of Notification for Withdrawal + References No definition available. + Details
Name: | slm_DepositsPeriodofNotificationforWithdrawal
Namespace Prefix: | slm_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Derivative Instrument, Percent of Total Notional Derivative Contracts + References No definition available. + Details
Name: | slm_DerivativeInstrumentPercentofTotalNotionalDerivativeContracts
Namespace Prefix: | slm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Discrete Tax Expense + References No definition available. + Details
Name: | slm_DiscreteTaxExpense
Namespace Prefix: | slm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition FFELP Loan Loss Confirmation Period + References No definition available. + Details
Name: | slm_FFELPLoanLossConfirmationPeriod
Namespace Prefix: | slm_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Financing Receivables, Modifications, Period of Interest Rate Reduction and Forbearance Usage + References No definition available. + Details
Name: | slm_FinancingReceivablesModificationsPeriodofInterestRateReductionandForbearanceUsage
Namespace Prefix: | slm_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Loan Delinquent Period + References No definition available. + Details
Name: | slm_LoanDelinquentPeriod
Namespace Prefix: | slm_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Loans And Leases Receivable, Temporary Interest Rate Reduction, Financial Difficulty Status + References No definition available. + Details
Name: | slm_LoansAndLeasesReceivableTemporaryInterestRateReductionFinancialDifficultyStatus
Namespace Prefix: | slm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Loans and Leases Receivable, Forbearance Period after Grace Period + References No definition available. + Details
Name: | slm_LoansandLeasesReceivableForbearancePeriodafterGracePeriod
Namespace Prefix: | slm_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Loans and Leases Receivable, Impaired, Loans Granted Forbearance Qualified as Trouble Debt Restructuring + References No definition available. + Details
Name: | slm_LoansandLeasesReceivableImpairedLoansGrantedForbearanceQualifiedasTroubleDebtRestructuring
Namespace Prefix: | slm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Loans and Leases Receivable, Period After Grace Period for Forbearance Allowance + References No definition available. + Details
Name: | slm_LoansandLeasesReceivablePeriodAfterGracePeriodforForbearanceAllowance
Namespace Prefix: | slm_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Loans and Leases Receivable, Period of Forbearance + References No definition available. + Details
Name: | slm_LoansandLeasesReceivablePeriodofForbearance
Namespace Prefix: | slm_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Loans and Leases Receivable, Period of Forbearance Within Twenty-Four Month Period to be Classified as TDR + References No definition available. + Details
Name: | slm_LoansandLeasesReceivablePeriodofForbearanceWithinTwentyFourMonthPeriodtobeClassifiedasTDR
Namespace Prefix: | slm_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Loans and Leases Receivable, Personal Loans Held at End of Year + References No definition available. + Details
Name: | slm_LoansandLeasesReceivablePersonalLoansHeldatEndofYear
Namespace Prefix: | slm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Percentage reimbursement on all qualifying default claims period one. + References No definition available. + Details
Name: | slm_PercentageReimbursementOnAllQualifyingDefaultClaimsPeriodOne
Namespace Prefix: | slm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Percentage reimbursement on all qualifying default claims period three. + References No definition available. + Details
Name: | slm_PercentageReimbursementOnAllQualifyingDefaultClaimsPeriodThree
Namespace Prefix: | slm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Percentage Reimbursement On All Qualifying FFELP Default Claims Period Two + References No definition available. + Details
Name: | slm_PercentageReimbursementOnAllQualifyingFfelpDefaultClaimsPeriodTwo
Namespace Prefix: | slm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Percentage of Private Education Loans related to borrowers inschool, grace or deferment + References No definition available. + Details
Name: | slm_PercentageofPrivateEducationLoansrelatedtoborrowersinschoolgraceordeferment
Namespace Prefix: | slm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Period After Last Payment Contractually Due Private Education Loan Considered To Be Delinquent + References No definition available. + Details
Name: | slm_PeriodAfterLastPaymentContractuallyDuePrivateEducationLoanConsideredToBeDelinquent
Namespace Prefix: | slm_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Period of Loss Emergence To Estimate Credit Losses Incurred + References No definition available. + Details
Name: | slm_PeriodofLossEmergenceToEstimateCreditLossesIncurred
Namespace Prefix: | slm_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Private Education Loan Loss Confirmation Period + References No definition available. + Details
Name: | slm_PrivateEducationLoanLossConfirmationPeriod
Namespace Prefix: | slm_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Private education loans net. + References No definition available. + Details
Name: | slm_PrivateEducationLoansNet
Namespace Prefix: | slm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of increase (decrease) in accumulated other comprehensive income (AOCI) for reclassification to retained earnings of tax effect from remeasurement of deferred tax pursuant to Tax Cuts and Jobs Act of 2017. + References No definition available. + Details
Name: | slm_TaxCutsAndJobsActOf2017ReclassificationFromAociToRetainedEarningsTaxEffect
Namespace Prefix: | slm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Variable Interest Entities, Option to Exercise, Maximum Percentage of Assets to Original Loan Balance + References No definition available. + Details
Name: | slm_VariableInterestEntitiesOptiontoExerciseMaximumPercentageofAssetstoOriginalLoanBalance
Namespace Prefix: | slm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_AccountsNotesAndLoansReceivableLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption. + References No definition available. + Details
Name: | us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319 + Details
Name: | us-gaap_DeferredTaxAssetsGross
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount, after deferred tax asset, of deferred tax liability attributable to taxable differences without jurisdictional netting. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 45 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=84176650&loc=d3e31931-109318 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319 + Details
Name: | us-gaap_DeferredTaxLiabilities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Fair values as of the balance sheet date of the net amount of all assets and liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958 + Details
Name: | us-gaap_DerivativeAssetsLiabilitiesAtFairValueNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5618551-113959 + Details
Name: | us-gaap_GainLossOnDerivativeInstrumentsNetPretax
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The net gain (loss) resulting from a sale of loans, including adjustments to record loans classified as held-for-sale at the lower-of-cost-or-market and fair value adjustments to loan held for investment purposes. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04.13(h)) -URI http://asc.fasb.org/extlink&oid=114873765&loc=SL114874048-224260 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.3(a)) -URI http://asc.fasb.org/extlink&oid=114873790&loc=SL114874131-224263 + Details
Name: | us-gaap_GainLossOnSalesOfLoansNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 22 -Subparagraph (h) -URI http://asc.fasb.org/extlink&oid=115929826&loc=d3e8736-108599 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08(h)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 20 -Section 45 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=109238882&loc=d3e38679-109324 + Details
Name: | us-gaap_IncomeTaxExpenseBenefit
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Carrying amount as of the balance sheet date of income taxes previously overpaid to tax authorities (such as U.S. Federal, state and local tax authorities) representing refunds of overpayments or recoveries based on agreed-upon resolutions of disputes. Also called income tax refund receivable. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(8)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(10)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 + Details
Name: | us-gaap_IncomeTaxReceivable
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount recognized for uncertainty in income taxes classified as current. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.20) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_LiabilityForUncertainTaxPositionsCurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Reflects the net positive or negative amount derived from subtracting from net proceeds of sale and the carrying amounts, net of allocated reserves, of financial assets transferred to third parties in transactions that qualify for sales treatment. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 20 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=109247956&loc=d3e107425-111719 + Details
Name: | us-gaap_LoansAndLeasesReceivableGainLossOnSalesNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition This is the result of the principal amount outstanding of total loans managed or securitized less securitized loans and loans that are in the process of being securitized. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=109247956&loc=d3e107314-111719 + Details
Name: | us-gaap_PrincipalAmountOutstandingOfLoansHeldInPortfolio
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=slm_SplitLoansMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=srt_AffiliatedEntityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=exch_XCME
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=slm_LondonClearingHouseMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementEquityComponentsAxis=us-gaap_RetainedEarningsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementEquityComponentsAxis=us-gaap_AccumulatedOtherComprehensiveIncomeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DisposalGroupClassificationAxis=us-gaap_DiscontinuedOperationsDisposedOfBySaleMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AdjustmentsForNewAccountingPronouncementsAxis=us-gaap_AccountingStandardsUpdate201712Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=us-gaap_FairValueHedgingMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=us-gaap_CashFlowHedgingMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_NewAccountingPronouncementEarlyAdoptionAxis=us-gaap_AccountingStandardsUpdate201609Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AdjustmentsForNewAccountingPronouncementsAxis=us-gaap_NewAccountingPronouncementMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |