| Document and Entity Information Document | Oct. 26, 2020 |
| Entity Information [Line Items] | |
| Document Type | 8-K |
| Document Period End Date | Oct. 26, 2020 |
| Entity Registrant Name | SLM CORP |
| Entity Central Index Key | 0001032033 |
| Amendment Flag | false |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-13251 |
| Entity Tax Identification Number | 52-2013874 |
| Entity Address, Address Line One | 300 Continental Drive |
| Entity Address, City or Town | Newark, |
| Entity Address, State or Province | DE |
| Entity Address, Postal Zip Code | 19713 |
| City Area Code | 302 |
| Local Phone Number | 451-0200 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | true |
| Entity Emerging Growth Company | false |
| Common Class A [Member] | |
| Entity Information [Line Items] | |
| Title of 12(b) Security | Common stock, par value $.20 per share |
| Trading Symbol | SLM |
| Security Exchange Name | NASDAQ |
| Noncumulative Preferred Stock [Member] | |
| Entity Information [Line Items] | |
| Title of 12(b) Security | Floating Rate Non-Cumulative Preferred Stock, Series B, par value $.20 per share |
| Trading Symbol | SLMBP |
| Security Exchange Name | NASDAQ |
