Revenue from Contracts with Clients - Narrative (Details)	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Revenue from Contract with Customer [Abstract]
Total revenues (percentage)	1.40%	1.40%	1.40%	0.90%
Operating revenues (percentage)	33.90%	35.80%	34.30%	37.60%