General - Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Operating results by business segment
Net revenue	$ 1,254,118	$ 1,170,117	$ 3,636,535	$ 3,392,571
Transferred at a point in time
Operating results by business segment
Net revenue	585,527	601,429	1,665,827	1,722,004
Transferred over time
Operating results by business segment
Net revenue	668,591	568,688	1,970,708	1,670,567
Government
Operating results by business segment
Net revenue	378,278	450,885	1,194,302	1,313,326
Non-government
Operating results by business segment
Net revenue	875,840	719,232	2,442,233	2,079,245
Behavioral & Specialty Health, risk-based, non-EAP
Operating results by business segment
Net revenue	437,731	352,347	1,240,284	1,046,209
Behavioral & Specialty Health, EAP risk-based
Operating results by business segment
Net revenue	75,369	74,703	245,634	232,060
Behavioral & Specialty Health, ASO
Operating results by business segment
Net revenue	78,837	73,887	248,033	216,050
PBM, including dispensing
Operating results by business segment
Net revenue	584,298	535,498	1,662,914	1,543,696
Medicare Part D
Operating results by business segment
Net revenue	1,229	65,931	2,913	178,308
PBA
Operating results by business segment
Net revenue	39,206	35,068	132,558	96,008
Formulary management
Operating results by business segment
Net revenue	34,734	31,327	96,979	78,550
Other service lines
Operating results by business segment
Net revenue	2,714	1,356	7,220	1,690
Healthcare
Operating results by business segment
Net revenue	580,278	489,451	1,698,427	1,459,378
Healthcare | Transferred over time
Operating results by business segment
Net revenue	580,278	489,451	1,698,427	1,459,378
Healthcare | Government
Operating results by business segment
Net revenue	235,636	240,845	741,252	690,340
Healthcare | Non-government
Operating results by business segment
Net revenue	344,642	248,606	957,175	769,038
Healthcare | Behavioral & Specialty Health, risk-based, non-EAP
Operating results by business segment
Net revenue	437,809	352,442	1,240,540	1,046,486
Healthcare | Behavioral & Specialty Health, EAP risk-based
Operating results by business segment
Net revenue	75,369	74,703	245,634	232,060
Healthcare | Behavioral & Specialty Health, ASO
Operating results by business segment
Net revenue	67,100	62,306	212,253	180,832
Pharmacy Management
Operating results by business segment
Net revenue	677,339	685,928	1,948,919	1,948,203
Pharmacy Management | Transferred at a point in time
Operating results by business segment
Net revenue	588,851	606,546	1,676,158	1,736,519
Pharmacy Management | Transferred over time
Operating results by business segment
Net revenue	88,488	79,382	272,761	211,684
Pharmacy Management | Government
Operating results by business segment
Net revenue	142,642	210,040	453,050	622,986
Pharmacy Management | Non-government
Operating results by business segment
Net revenue	534,697	475,888	1,495,869	1,325,217
Pharmacy Management | Behavioral & Specialty Health, ASO
Operating results by business segment
Net revenue	11,834	11,631	36,004	35,436
Pharmacy Management | PBM, including dispensing
Operating results by business segment
Net revenue	587,622	540,615	1,673,245	1,558,211
Pharmacy Management | Medicare Part D
Operating results by business segment
Net revenue	1,229	65,931	2,913	178,308
Pharmacy Management | PBA
Operating results by business segment
Net revenue	39,206	35,068	132,558	96,008
Pharmacy Management | Formulary management
Operating results by business segment
Net revenue	34,734	31,327	96,979	78,550
Pharmacy Management | Other service lines
Operating results by business segment
Net revenue	2,714	1,356	7,220	1,690
Elimination
Operating results by business segment
Net revenue	(3,499)	(5,262)	(10,811)	(15,010)
Elimination | Transferred at a point in time
Operating results by business segment
Net revenue	(3,324)	(5,117)	(10,331)	(14,515)
Elimination | Transferred over time
Operating results by business segment
Net revenue	(175)	(145)	(480)	(495)
Elimination | Non-government
Operating results by business segment
Net revenue	(3,499)	(5,262)	(10,811)	(15,010)
Elimination | Behavioral & Specialty Health, risk-based, non-EAP
Operating results by business segment
Net revenue	(78)	(95)	(256)	(277)
Elimination | Behavioral & Specialty Health, ASO
Operating results by business segment
Net revenue	(97)	(50)	(224)	(218)
Elimination | PBM, including dispensing
Operating results by business segment
Net revenue	$ (3,324)	$ (5,117)	$ (10,331)	$ (14,515)