Business Segment Information - Reconciliation of Segment Operating Income to Income From Continuing Operations (Details) - USD ($)	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Operating income	$ (6,113,137,000)	$ 404,831,000	$ 309,515,000	$ 263,437,000	$ 179,841,000	$ 406,694,000	$ 47,565,000	$ 477,823,000	$ (5,135,354,000)	$ 1,111,923,000	$ 1,443,685,000
Gain from antitrust litigation settlements	500,000		100,000	8,500,000	3,100,000	3,500,000	52,000,000.0	87,300,000	9,100,000	145,900,000	35,900,000
LIFO (expense) credit	35,800,000	(6,100,000)	(23,900,000)	(13,300,000)	(57,200,000)	9,900,000	66,800,000	3,000,000.0	(7,422,000)	22,544,000	(67,324,000)
PharMEDium remediation costs				(7,100,000)	(6,700,000)	(11,700,000)	(12,300,000)	(17,900,000)
PharMEDium shutdown costs		(400,000)	(5,000,000.0)
Contingent consideration adjustment									12,153,000	0	0
Employee severance, litigation, and other									(6,807,307,000)	(330,474,000)	(183,520,000)
Goodwill impairment									0	0	(59,684,000)
Impairment of long-lived assets	$ 0	0	$ (223,652,000)	$ (138,000,000)	$ 0	$ 0	$ (570,000,000)	$ 0	(361,652,000)	(570,000,000)	0
Other (income) loss									(1,581,000)	(12,952,000)	25,469,000
Interest expense, net									137,883,000	157,769,000	174,699,000
Loss on consolidation of equity investments									0	0	42,328,000
Loss on early retirement of debt		$ (22,200,000)							22,175,000	0	23,766,000
(Loss) income before income taxes									(5,293,831,000)	967,106,000	1,177,423,000
Operating segments
Segment Reporting Information [Line Items]
Operating income									2,204,447,000	2,051,252,000	1,981,230,000
Segment reconciling items
Segment Reporting Information [Line Items]
Gain from antitrust litigation settlements									9,076,000	145,872,000	35,938,000
LIFO (expense) credit									(7,422,000)	22,544,000	(67,324,000)
PharMEDium remediation costs									(16,165,000)	(69,423,000)	(66,204,000)
PharMEDium shutdown costs									(43,206,000)	0	0
New York State Opioid Stewardship Act									(14,800,000)	22,000,000	(22,000,000)
Acquisition-related intangibles amortization									(110,478,000)	(159,848,000)	(174,751,000)
Employee severance, litigation, and other									(6,807,307,000)	(330,474,000)	(183,520,000)
Goodwill impairment									0	0	(59,684,000)
Impairment of long-lived assets									$ (361,652,000)	$ (570,000,000)	$ 0