Pension and Postretirement Plans - Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Jun. 30, 2018	Jun. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	$ 0	$ 45	$ (18)	$ (117)	$ 0	$ (90)
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0			1	1
Interest cost	2	1			5	4
Expected return on plan assets	(2)	(2)			(7)	(7)
Net periodic benefit credit	0	(1)			(1)	(2)
UNITED STATES | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	4	4			11	13
Interest cost	27	28			80	85
Expected return on plan assets	(58)	(57)			(172)	(174)
Net actuarial (gain) loss	0	45			0	(90)
Settlement (gain) loss	0	1			0	(8)
Net periodic benefit credit	(27)	21			(81)	(174)
Non-U.S. | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	6	8			18	24
Interest cost	14	13			43	36
Expected return on plan assets	(29)	(23)			(87)	(68)
Net periodic benefit credit	$ (9)	$ (2)			$ (26)	$ (8)