Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Sep. 30, 2020
Fair Value [Line Items]
Fair value of long term debt	$ 8,300		$ 8,300		$ 8,600
Fair Value, Inputs, Level 1 [Member]
Fair Value [Line Items]
Fair value of long term debt	8,100		8,100		8,400
Fair Value, Inputs, Level 2 [Member]
Fair Value [Line Items]
Fair value of long term debt	200		200		$ 200
Deferred compensation plan assets [Member]
Fair Value [Line Items]
Unrealized gains (losses)	0	$ 6	7	$ (1)
Exchange Traded Funds
Fair Value [Line Items]
Unrealized gains (losses)	$ 16	$ 31	$ 39	$ 9