Significant Accounting Policies	9 Months Ended
Sep. 30, 2017
Accounting Policies [Abstract]
Significant Accounting Policies	Significant Accounting Policies 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, 2017 are not necessarily indicative of the results for the year ending December 31, 2017 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, 2016 (the “2016 Form 10-K”). 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. Allowance for Loan Losses We maintain an allowance for loan losses at an amount sufficient to absorb probable losses incurred in our portfolios at the reporting date based on a projection of estimated probable credit losses incurred in the portfolio. Please refer to Note 2, “Significant Accounting Policies - Allowance for Loan Losses - Allowance for Private Education Loan Losses” in the 2016 Form 10-K for a description of certain information we use in estimating allowance amounts for Private Education Loans (as hereafter defined). Troubled Debt Restructurings (“TDRs”) For our TDR portfolio, we estimate an allowance amount sufficient to cover life-of-loan expected losses through an impairment calculation based on the difference between the loan’s basis and the present value of expected future cash flows (which would include life-of-loan default and recovery assumptions) discounted at the loan’s original effective interest rate. Our TDR portfolio is comprised mostly of loans with interest rate reductions and loans with forbearance usage greater than three months, as further described below. We modify the terms of loans for certain borrowers when we believe such modifications may increase the ability and willingness of a borrower to make payments and thus increase the ultimate overall amount collected on a loan. These modifications generally take the form of a forbearance, a temporary interest rate reduction or an extended repayment plan. We generally consider a loan that is in full principal and interest repayment status which has received more than three months of forbearance in a 24-month period to be a TDR; however, during the first nine months after a loan has entered full principal and interest repayment status, we do not count up to the first six months of forbearance received during that period against the three-month policy limit. A loan also becomes a TDR when it is modified to reduce the interest rate on the loan (regardless of when such modification occurs and/or whether such interest rate reduction is temporary). The majority of our loans that are considered TDRs involve a temporary forbearance of payments and do not change the contractual interest rate of the loan. Once a loan qualifies for TDR status, it remains a TDR for allowance purposes for the remainder of its life. As of September 30, 2017 and December 31, 2016, approximately 69 percent of TDRs were classified as such due to their forbearance status. Derivative Accounting We account for our derivatives, consisting of interest rate swaps, at fair value on the consolidated balance sheets as either an asset or liability. Derivative positions are recorded as net positions by counterparty based on master netting arrangements (see Note 6, “Derivative Financial Instruments”), exclusive of accrued interest and cash collateral held or pledged. The Chicago Mercantile Exchange (“CME”) and the London Clearing House (“LCH”) made amendments to their respective rules that resulted in the prospective accounting treatment of certain daily payments historically treated as the posting of collateral (variation margin payments) being considered as the legal settlement of the outstanding exposure of the derivative. While the CME rule, which became effective in January 2017, is mandatory, the LCH allows a clearing member institution the option to adopt the rule changes on an individual contract or portfolio basis. As of September 30, 2017, $5.1 billion notional of our derivative contracts were cleared on the CME and $0.7 billion were cleared on the LCH. The derivative contracts cleared through the CME and LCH represent 85.8 percent and 11.9 percent, respectively, of our total notional derivative contracts of $5.9 billion at September 30, 2017. Under this new rule, for derivatives cleared through the CME, the net gain (loss) position includes the variation margin amounts as settlement of the derivative and not collateral against the fair value of the derivative. Interest income (expense) related to variation margin on derivatives that are not designated as hedging instruments or are designated as fair value relationships is recognized as a gain (loss) rather than as interest income (expense). Changes in fair value for derivatives not designated as hedging instruments will be presented as realized gains (losses). Our LCH clearing member institution has elected not to adopt the new rule change. Therefore, there has been no change to the accounting for the derivatives cleared through the LCH, and variation margin payments required to be exchanged based on the fair value of these derivatives remain accounted for as collateral. We determine the fair value for our derivative contracts primarily using pricing models that consider current market conditions and the contractual terms of the derivative contracts. These pricing models consider interest rates, time value, forward interest rate curves, and volatility factors. Inputs are generally from active financial markets. The majority of our derivatives qualify as effective hedges. For these derivatives, the relationship between the hedging instrument and the hedged items (including the hedged risk and method for assessing effectiveness), as well as the risk management objective and strategy for undertaking various hedge transactions at the inception of the hedging relationship, is documented. Each derivative is designated to a specific (or pool of) liability(ies) on the consolidated balance sheets, and is designated as either a “fair value” hedge or a “cash flow” hedge. Fair value hedges are designed to hedge our exposure to the changes in fair value of a fixed-rate liability. For effective fair value hedges, both the hedge and the hedged item (for the risk being hedged) are recorded at fair value with any difference reflecting ineffectiveness recorded immediately in the consolidated statements of income. Cash flow hedges are designed to hedge our exposure to variability in cash flows related to variable-rate deposits. The assessment of the hedge’s effectiveness is performed at inception and on an ongoing basis, using regression testing. For hedges of a pool of liabilities, tests are performed to demonstrate the similarity of individual instruments of the pool. When it is determined that a derivative is not currently an effective hedge, ineffectiveness is recognized for the full change in fair value of the derivative with no offsetting amount from the hedged item since the last time it was effective. If it is also determined the hedge will not be effective in the future, we discontinue the hedge accounting prospectively and begin amortization of any basis adjustments that exist related to the hedged item. Stock-Based Compensation We recognize stock-based compensation cost in our consolidated statements of income using the fair value method. Under this method, we determine the fair value of the stock-based compensation at the time of the grant and recognize the resulting compensation expense over the vesting period of the stock-based grant. On January 1, 2017, we adopted the Financial Accounting Standards Board’s (“FASB’s”) Accounting Standards Update (“ASU”) 2016-09 “Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting.” This new guidance requires that we record all excess tax benefits/deficiencies related to the settlement of employee stock-based compensation to the income tax expense line item on our consolidated statements of income, under a modified retrospective basis. In the nine months ended September 30, 2017, we recorded a $7.3 million benefit in income tax expense because of this new standard. We previously recorded the excess tax benefits/deficiencies to the additional paid-in capital line item on our consolidated balance sheets. Under the new guidance, we also elected the option to no longer apply a forfeiture rate to our stock-based compensation expense, but to record forfeitures when they occur, and, as a result, under a modified retrospective basis we recorded a cumulative effect of the new stock compensation standard in total equity of $0.2 million, net of tax, in the first quarter of 2017. Recently Issued but Not Yet Adopted Accounting Pronouncements On August 28, 2017, the FASB issued ASU 2017-12, “Derivatives and Hedging: Targeted Improvements to Accounting for Hedging Activities,” which improves the financial reporting of hedging relationships to better portray the economic results of an entity's risk management activities in its financial statements and make certain targeted improvements to simplify the application of the hedge accounting guidance. The guidance expands the ability to hedge nonfinancial and financial risk components, reduces complexity in fair value hedges of interest rate risk, eliminates the requirement to separately measure and report hedge ineffectiveness, as well as eases certain hedge effectiveness assessment requirements. The effective date for the standard is January 1, 2019, with early adoption permitted. We are currently evaluating if we will adopt this standard prior to its final effective date, and we currently do not expect the adoption to materially affect our consolidated financial statements.

Significant Accounting Policies

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, 2017 are not necessarily indicative of the results for the year ending December 31, 2017 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, 2016 (the “2016 Form 10-K”).

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.

Allowance for Loan Losses

We maintain an allowance for loan losses at an amount sufficient to absorb probable losses incurred in our portfolios at the reporting date based on a projection of estimated probable credit losses incurred in the portfolio. Please refer to Note 2, “Significant Accounting Policies - Allowance for Loan Losses - Allowance for Private Education Loan Losses” in the 2016 Form 10-K for a description of certain information we use in estimating allowance amounts for Private Education Loans (as hereafter defined).

Troubled Debt Restructurings (“TDRs”)

For our TDR portfolio, we estimate an allowance amount sufficient to cover life-of-loan expected losses through an impairment calculation based on the difference between the loan’s basis and the present value of expected future cash flows (which would include life-of-loan default and recovery assumptions) discounted at the loan’s original effective interest rate. Our TDR portfolio is comprised mostly of loans with interest rate reductions and loans with forbearance usage greater than three months, as further described below.

We modify the terms of loans for certain borrowers when we believe such modifications may increase the ability and willingness of a borrower to make payments and thus increase the ultimate overall amount collected on a loan. These modifications generally take the form of a forbearance, a temporary interest rate reduction or an extended repayment plan. We generally consider a loan that is in full principal and interest repayment status which has received more than three months of forbearance in a 24-month period to be a TDR; however, during the first nine months after a loan has entered full principal and interest repayment status, we do not count up to the first six months of forbearance received during that period against the three-month policy limit.

A loan also becomes a TDR when it is modified to reduce the interest rate on the loan (regardless of when such modification occurs and/or whether such interest rate reduction is temporary). The majority of our loans that are considered TDRs involve a temporary forbearance of payments and do not change the contractual interest rate of the loan. Once a loan qualifies for TDR status, it remains a TDR for allowance purposes for the remainder of its life. As of September 30, 2017 and December 31, 2016, approximately 69 percent of TDRs were classified as such due to their forbearance status.

Derivative Accounting

We account for our derivatives, consisting of interest rate swaps, at fair value on the consolidated balance sheets as either an asset or liability. Derivative positions are recorded as net positions by counterparty based on master netting arrangements (see Note 6, “Derivative Financial Instruments”), exclusive of accrued interest and cash collateral held or pledged. The Chicago Mercantile Exchange (“CME”) and the London Clearing House (“LCH”) made amendments to their respective rules that resulted in the prospective accounting treatment of certain daily payments historically treated as the posting of collateral (variation margin payments) being considered as the legal settlement of the outstanding exposure of the derivative. While the CME rule, which became effective in January 2017, is mandatory, the LCH allows a clearing member institution the option to adopt the rule changes on an individual contract or portfolio basis. As of September 30, 2017, $5.1 billion notional of our derivative contracts were cleared on the CME and $0.7 billion were cleared on the LCH. The derivative contracts cleared through the CME and LCH represent 85.8 percent and 11.9 percent, respectively, of our total notional derivative contracts of $5.9 billion at September 30, 2017.

Under this new rule, for derivatives cleared through the CME, the net gain (loss) position includes the variation margin amounts as settlement of the derivative and not collateral against the fair value of the derivative. Interest income (expense) related to variation margin on derivatives that are not designated as hedging instruments or are designated as fair value relationships is recognized as a gain (loss) rather than as interest income (expense). Changes in fair value for derivatives not designated as hedging instruments will be presented as realized gains (losses).

Our LCH clearing member institution has elected not to adopt the new rule change. Therefore, there has been no change to the accounting for the derivatives cleared through the LCH, and variation margin payments required to be exchanged based on the fair value of these derivatives remain accounted for as collateral.

We determine the fair value for our derivative contracts primarily using pricing models that consider current market conditions and the contractual terms of the derivative contracts. These pricing models consider interest rates, time value, forward interest rate curves, and volatility factors. Inputs are generally from active financial markets.

The majority of our derivatives qualify as effective hedges. For these derivatives, the relationship between the hedging instrument and the hedged items (including the hedged risk and method for assessing effectiveness), as well as the risk management objective and strategy for undertaking various hedge transactions at the inception of the hedging relationship, is documented.

Each derivative is designated to a specific (or pool of) liability(ies) on the consolidated balance sheets, and is designated as either a “fair value” hedge or a “cash flow” hedge. Fair value hedges are designed to hedge our exposure to the changes in fair value of a fixed-rate liability. For effective fair value hedges, both the hedge and the hedged item (for the risk being hedged) are recorded at fair value with any difference reflecting ineffectiveness recorded immediately in the consolidated statements of income. Cash flow hedges are designed to hedge our exposure to variability in cash flows related to variable-rate deposits. The assessment of the hedge’s effectiveness is performed at inception and on an ongoing basis, using regression testing. For hedges of a pool of liabilities, tests are performed to demonstrate the similarity of individual instruments of the pool. When it is determined that a derivative is not currently an effective hedge, ineffectiveness is recognized for the full change in fair value of the derivative with no offsetting amount from the hedged item since the last time it was effective. If it is also determined the hedge will not be effective in the future, we discontinue the hedge accounting prospectively and begin amortization of any basis adjustments that exist related to the hedged item.

Stock-Based Compensation

We recognize stock-based compensation cost in our consolidated statements of income using the fair value method. Under this method, we determine the fair value of the stock-based compensation at the time of the grant and recognize the resulting compensation expense over the vesting period of the stock-based grant. On January 1, 2017, we adopted the Financial Accounting Standards Board’s (“FASB’s”) Accounting Standards Update (“ASU”) 2016-09 “Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting.” This new guidance requires that we record all excess tax benefits/deficiencies related to the settlement of employee stock-based compensation to the income tax expense line item on our consolidated statements of income, under a modified retrospective basis. In the nine months ended September 30, 2017, we recorded a $7.3 million benefit in income tax expense because of this new standard. We previously recorded the excess tax benefits/deficiencies to the additional paid-in capital line item on our consolidated balance sheets. Under the new guidance, we also elected the option to no longer apply a forfeiture rate to our stock-based compensation expense, but to record forfeitures when they occur, and, as a result, under a modified retrospective basis we recorded a cumulative effect of the new stock compensation standard in total equity of $0.2 million, net of tax, in the first quarter of 2017.

Recently Issued but Not Yet Adopted Accounting Pronouncements

On August 28, 2017, the FASB issued ASU 2017-12, “Derivatives and Hedging: Targeted Improvements to Accounting for Hedging Activities,” which improves the financial reporting of hedging relationships to better portray the economic results of an entity's risk management activities in its financial statements and make certain targeted improvements to simplify the application of the hedge accounting guidance. The guidance expands the ability to hedge nonfinancial and financial risk components, reduces complexity in fair value hedges of interest rate risk, eliminates the requirement to separately measure and report hedge ineffectiveness, as well as eases certain hedge effectiveness assessment requirements. The effective date for the standard is January 1, 2019, with early adoption permitted. We are currently evaluating if we will adopt this standard prior to its final effective date, and we currently do not expect the adoption to materially affect our consolidated financial statements.