Cover Page - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2019	Jan. 31, 2020	Jun. 30, 2019
Document Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2019
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 Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 4.1
Entity Common Stock, Shares Outstanding (in shares)		422,615,193
Documents Incorporated by Reference	Portions of the proxy statement relating to the Registrant’s 2020 Annual Meeting of Stockholders are incorporated by reference into Part III of this Annual Report on Form 10-K.
Amendment Flag	false
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Entity Central Index Key	0001032033
Current Fiscal Year End Date	--12-31
Common Stock
Document 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
Document 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