Significant Accounting Policies (Policies)	9 Months Ended
Significant Accounting Policies (Policies)	Sep. 30, 2016
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited, consolidated financial statements of SLM Corporation (“Sallie Mae,” “SLM,” the “Company,” “we,” or “us”) have been prepared in accordance with generally accepted accounting principles in the United States of America (“GAAP”) for interim financial information. Accordingly, they do not include all the information and footnotes required by GAAP for complete consolidated financial statements. The consolidated financial statements include the accounts of SLM Corporation and its majority-owned and controlled subsidiaries after eliminating the effects of intercompany accounts and transactions. In the opinion of management, all adjustments considered necessary for a fair statement of the results for the interim periods have been included. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Actual results could differ from those estimates. Operating results for the three and nine months ended September 30, 2016 are not necessarily indicative of the results for the year ending December 31, 2016 or for any other period. These unaudited financial statements should be read in conjunction with the audited financial statements and related notes included in our Annual Report on Form 10-K for the year ended December 31, 2015 (the “2015 Form 10-K”).
Consolidation	Consolidation The consolidated financial statements include the accounts of the Company and its majority-owned and controlled subsidiaries after eliminating the effects of intercompany accounts and transactions. We consolidate any variable interest entity (“VIE”) where we have determined we are the primary beneficiary. The primary beneficiary is the entity which has both: (1) the power to direct the activities of the VIE that most significantly impact the VIE’s economic performance and (2) the obligation to absorb losses or receive benefits of the entity that could potentially be significant to the VIE.
Loan Interest Income	Loan Interest Income For loans classified as “held for investment,” we recognize interest income as earned, adjusted for the amortization of deferred direct origination costs. This adjustment is recognized based upon the expected yield of the loan over its life after giving effect to prepayments and extensions. We consider our constant prepayment rate (“CPR”) estimates a significant accounting assumption used to measure the expected prepayment activity in our education loan portfolio. The estimates are based on a number of factors such as historical prepayment rates for loans with similar loan characteristics, assumptions about portfolio composition and loan terms, and the prepayment curve’s tendency to follow a ramp pattern (i.e., the prepayment rate typically increases during the in-school and early repayment periods, then stabilizes). The CPR measures the expected prepayment activity over the life of the loan and is applied as a flat-rate input assumption when used in forecasting. Our CPR estimates include the effect of voluntary prepayments, education loan defaults, and consolidation (if the loans are consolidated to third parties), all of which shorten the lives of loans. CPR estimates also consider the utilization of deferment, forbearance, and extended repayment plans, which lengthen the lives of loans. We regularly evaluate the assumptions used to estimate the CPRs. In instances where there are changes to the assumptions, amortization of deferred direct origination costs is adjusted on a cumulative basis to reflect the change since the origination of the loan. We also pay to the U.S. Department of Education (“ED”) an annual 105 basis point Consolidation Loan Rebate Fee on FFELP consolidation loans, which is netted against loan interest income. Additionally, interest earned on education loans reflects potential non-payment adjustments in accordance with our uncollectible interest recognition policy. We do not amortize any adjustments to the basis of education loans when they are classified as “held-for-sale.” We recognize certain fee income (primarily late fees) on education loans when earned according to the contractual provisions of the promissory notes, as well as our expectation of collectibility. Fee income is recorded when earned in “other non-interest income” in the accompanying consolidated statements of income.
Recently Issued but Not Yet Adopted Accounting Pronouncements	Recently Issued but Not Yet Adopted Accounting Pronouncements On February 25, 2016, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update (“ASU”) No. 2016-02, “Leases,” a comprehensive new lease standard which will supersede previous lease guidance. The standard requires a lessee to recognize in its balance sheet assets and liabilities related to long-term leases that were classified as operating leases under previous guidance. An asset will be recognized related to the right to use the underlying asset and a liability will be recognized related to the obligation to make lease payments over the term of the lease. The standard also requires expanded disclosures surrounding leases. The standard is effective for fiscal periods beginning after December 15, 2018, and requires modified retrospective adoption, with early adoption permitted. We are currently evaluating the impact of the adoption of this standard on our consolidated financial statements and related disclosures. On March 30, 2016, the FASB issued ASU No. 2016-09, “Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting,” which amends the current stock compensation guidance. The amendments simplify the accounting for the taxes related to stock-based compensation, including adjustments to how excess tax benefits and a company’s payments for tax withholdings should be classified. The standard is effective for fiscal periods beginning after December 15, 2016, with early adoption permitted. We continue to evaluate the impact of the adoption of this standard on our consolidated financial statements, and at this time we expect the standard to result in immaterial volatility in earnings caused by the change in the treatment of the tax benefits or deficiencies related to share-based payments at settlement (or expiration) through “income tax expense” in our consolidated statements of income. On June 16, 2016, the FASB issued ASU No. 2016-13, “Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments,” which requires measurement and recognition of expected credit losses for financial assets held. Under this standard, we will be required to hold an allowance equal to the expected life-of-loan losses on our loan portfolio. The standard is effective for fiscal periods beginning after December 15, 2019. While we are currently evaluating the impact of our pending adoption of this standard on our consolidated financial statements, we expect the adoption to have a material impact on our consolidated financial statements and capital ratios.