Pension and Other Postretirement Benefits - Benefit Obligations in Excess of Plan Assets (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
U.S. Plans
Accumulated benefit obligation in excess of plan assets
Accumulated benefit obligation at end of period	$ (7)	$ (7)
Fair value of plan assets at end of period	0	0
Projected benefit obligation in excess of plan assets
Benefit obligation at end of period	(7)	(7)
Fair value of plan assets at end of period	0	0
Non-U.S. Plans
Accumulated benefit obligation in excess of plan assets
Accumulated benefit obligation at end of period	(563)	(528)
Fair value of plan assets at end of period	525	490
Projected benefit obligation in excess of plan assets
Benefit obligation at end of period	(563)	(528)
Fair value of plan assets at end of period	$ 525	$ 490