Business Segment Information - Reconciliation of Segment Operating Income to Income (Loss) from Operations before Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Operating income	$ 404,831	$ 406,694	$ 977,783	$ 932,082
Gain from antitrust litigation settlements		3,500	8,500	142,700
LIFO (expense) credit			(43,195)	79,747
Employee severance, litigation, and other	(58,585)	(60,006)	(165,626)	(156,067)
Impairment of PharMEDium assets	0	0	(361,652)	(570,000)
Other loss (income), net	1,073	(342)	2,806	(11,739)
Interest expense, net	37,748	35,921	103,176	121,366
Loss on early retirement of debt	22,175	0	22,175	0
Income before income taxes	343,835	371,115	849,626	822,455
Operating segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Operating income	507,522	506,675	1,674,473	1,595,173
Segment reconciling items
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Gain from antitrust litigation settlements	0	3,480	8,546	142,735
LIFO (expense) credit	(6,061)	9,913	(43,195)	79,747
PharMEDium remediation costs	0	(19,344)	(16,165)	(55,736)
PharMEDium shutdown costs	(12,936)	0	(45,406)	0
New York State Opioid Stewardship Act	0	0	0	22,000
Contingent consideration adjustment	0	0	12,153	0
Acquisition-related intangibles amortization	(25,109)	(34,024)	(85,345)	(125,770)
Employee severance, litigation, and other	(58,585)	(60,006)	(165,626)	(156,067)
Impairment of PharMEDium assets	$ 0	$ 0	$ (361,652)	$ (570,000)