Document and Entity Information - USD ($) $ / shares in Units, $ in Billions	12 Months Ended
	Dec. 31, 2020	Feb. 19, 2021	Jun. 30, 2020
Cover [Abstract]
Entity Central Index Key	0000019411
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Document Transition Report	false
Entity File Number	1-6639
Entity Registrant Name	MAGELLAN HEALTH, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	58-1076937
Entity Address, Address Line One	4801 E. Washington Street
Entity Address, City or Town	Phoenix
Entity Address, State or Province	AZ
Entity Address, Postal Zip Code	85034
City Area Code	800
Local Phone Number	642-1716
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
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Listing, Par Value Per Share	$ 0.01
Title of 12(b) Security	Common Stock, par value $0.01 per share
Trading Symbol	MGLN
Security Exchange Name	NASDAQ
Entity Public Float			$ 1.8
Entity Common Stock, Shares Outstanding		25,965,579
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Amendment Flag	false