Business Segment Information - Segment Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue	$ 45,239,265	$ 43,142,309	$ 133,951,319	$ 124,642,499
Intersegment eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue	(22,825)	(36,780)	(67,683)	(66,970)
Pharmaceutical Distribution Services | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue	43,527,552	41,581,866	128,948,097	119,972,917
Other: | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue	1,734,538	1,597,223	5,070,905	4,736,552
MWI Animal Health | Other: | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue	1,021,936	945,342	2,923,813	2,836,917
Global Commercialization Services | Other: | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue	$ 712,602	$ 651,881	$ 2,147,092	$ 1,899,635