Cover page	3 Months Ended
	Mar. 31, 2020 shares
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2020
Document Transition Report	false
Entity File Number	001-13251
Entity Registrant Name	SLM Corp
Entity Incorporation, State or Country Code	DE
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
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Smaller Reporting Company	false
Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding	375,088,960
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Entity Central Index Key	0001032033
Current Fiscal Year End Date	--12-31
Common Stock
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
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