Business Segment Information - Segment Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue	$ 45,392,452	$ 40,466,332
Intersegment eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue	(22,867)	(16,317)
Pharmaceutical Distribution Services | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue	43,744,381	38,937,698
Other: | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue	1,670,938	1,544,951
MWI Animal Health | Other: | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue	954,584	958,572
Global Commercialization Services | Other: | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue	$ 716,354	$ 586,379