Business Segment Information - Segment Operating Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting Information [Line Items]
Total segment operating income	$ 404,831	$ 406,694	$ 977,783	$ 932,082
Operating segments
Segment Reporting Information [Line Items]
Total segment operating income	507,522	506,675	1,674,473	1,595,173
Intersegment eliminations
Segment Reporting Information [Line Items]
Total segment operating income	(1,996)	(142)	(2,575)	(698)
Pharmaceutical Distribution Services | Operating segments
Segment Reporting Information [Line Items]
Total segment operating income	426,643	411,707	1,381,434	1,301,948
Other | Operating segments
Segment Reporting Information [Line Items]
Total segment operating income	$ 82,875	$ 95,110	$ 295,614	$ 293,923