General - Revenue Recognition and ASU 2018-02 (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Operating results by business segment
Net revenue	$ 1,788,336	$ 1,810,923	$ 3,527,825	$ 3,616,000
Transferred at a point in time
Operating results by business segment
Net revenue	505,193		1,020,703
Transferred over time
Operating results by business segment
Net revenue	1,283,143		2,507,122
PBM, including dispensing
Operating results by business segment
Net revenue	435,350
Medicare Part D
Operating results by business segment
Net revenue	69,843
PBA
Operating results by business segment
Net revenue	33,476
Formulary management
Operating results by business segment
Net revenue	18,426
Other service lines
Operating results by business segment
Net revenue	419
Behavioral & Specialty Health | Risk-based, non-EAP
Operating results by business segment
Net revenue	400,526		762,256
Behavioral & Specialty Health | EAP risk-based
Operating results by business segment
Net revenue	87,296		176,913
Behavioral & Specialty Health | ASO
Operating results by business segment
Net revenue	68,240		131,495
Magellan Complete Care
Operating results by business segment
Net revenue			3,527,825
Magellan Complete Care | Risk-based, non-EAP
Operating results by business segment
Net revenue	659,362		1,301,933
Magellan Complete Care | ASO
Operating results by business segment
Net revenue	15,398		30,452
Magellan Complete Care | PBM, including dispensing
Operating results by business segment
Net revenue			887,520
Magellan Complete Care | Medicare Part D
Operating results by business segment
Net revenue			133,183
Magellan Complete Care | PBA
Operating results by business segment
Net revenue			67,453
Magellan Complete Care | Formulary management
Operating results by business segment
Net revenue			35,609
Magellan Complete Care | Other service lines
Operating results by business segment
Net revenue			1,011
Government
Operating results by business segment
Net revenue	1,084,347		2,200,888
Non-government
Operating results by business segment
Net revenue	703,989		1,326,937
Healthcare
Operating results by business segment
Net revenue	1,220,642		2,384,895
Healthcare | Transferred over time
Operating results by business segment
Net revenue	1,220,642		2,384,895
Healthcare | Behavioral & Specialty Health | Risk-based, non-EAP
Operating results by business segment
Net revenue	400,591		762,399
Healthcare | Behavioral & Specialty Health | EAP risk-based
Operating results by business segment
Net revenue	87,296		176,913
Healthcare | Behavioral & Specialty Health | ASO
Operating results by business segment
Net revenue	57,995		113,198
Healthcare | Magellan Complete Care
Operating results by business segment
Net revenue			2,384,895
Healthcare | Magellan Complete Care | Risk-based, non-EAP
Operating results by business segment
Net revenue	659,362		1,301,933
Healthcare | Magellan Complete Care | ASO
Operating results by business segment
Net revenue	15,398		30,452
Healthcare | Government
Operating results by business segment
Net revenue	910,543		1,799,036
Healthcare | Non-government
Operating results by business segment
Net revenue	310,099		585,859
Pharmacy Management
Operating results by business segment
Net revenue	612,658		1,229,118
Pharmacy Management | Transferred at a point in time
Operating results by business segment
Net revenue	550,010		1,106,575
Pharmacy Management | Transferred over time
Operating results by business segment
Net revenue	62,648		122,543
Pharmacy Management | PBM, including dispensing
Operating results by business segment
Net revenue	480,167
Pharmacy Management | Medicare Part D
Operating results by business segment
Net revenue	69,843
Pharmacy Management | PBA
Operating results by business segment
Net revenue	33,476
Pharmacy Management | Formulary management
Operating results by business segment
Net revenue	18,426
Pharmacy Management | Other service lines
Operating results by business segment
Net revenue	419
Pharmacy Management | Behavioral & Specialty Health | ASO
Operating results by business segment
Net revenue	10,327		18,470
Pharmacy Management | Magellan Complete Care
Operating results by business segment
Net revenue			1,229,118
Pharmacy Management | Magellan Complete Care | PBM, including dispensing
Operating results by business segment
Net revenue			973,392
Pharmacy Management | Magellan Complete Care | Medicare Part D
Operating results by business segment
Net revenue			133,183
Pharmacy Management | Magellan Complete Care | PBA
Operating results by business segment
Net revenue			67,453
Pharmacy Management | Magellan Complete Care | Formulary management
Operating results by business segment
Net revenue			35,609
Pharmacy Management | Magellan Complete Care | Other service lines
Operating results by business segment
Net revenue			1,011
Pharmacy Management | Government
Operating results by business segment
Net revenue	173,804		401,852
Pharmacy Management | Non-government
Operating results by business segment
Net revenue	$ 438,854		827,266
Elimination
Operating results by business segment
Net revenue		(44,964)	(86,188)
Elimination | Transferred at a point in time
Operating results by business segment
Net revenue		(44,817)	(85,872)
Elimination | Transferred over time
Operating results by business segment
Net revenue		(147)	(316)
Elimination | PBM, including dispensing
Operating results by business segment
Net revenue		(44,817)
Elimination | Behavioral & Specialty Health | Risk-based, non-EAP
Operating results by business segment
Net revenue		(65)	(143)
Elimination | Behavioral & Specialty Health | ASO
Operating results by business segment
Net revenue		(82)	(173)
Elimination | Magellan Complete Care
Operating results by business segment
Net revenue			(86,188)
Elimination | Magellan Complete Care | PBM, including dispensing
Operating results by business segment
Net revenue			(85,872)
Elimination | Non-government
Operating results by business segment
Net revenue		$ (44,964)	$ (86,188)