Pension and Postretirement Plans - Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2018	Mar. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Net actuarial gain	$ 0	$ (18)	$ (117)	$ 0	$ (135)
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	0		1	1
Interest cost	1	2		3	3
Expected return on plan assets	(3)	(2)		(5)	(5)
Net periodic benefit credit	(1)	0		(1)	(1)
UNITED STATES | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	3	4		7	9
Interest cost	27	29		53	57
Expected return on plan assets	(57)	(58)		(114)	(117)
Net actuarial gain	0	(18)		0	(135)
Settlement gain	0	(1)		0	(9)
Net periodic benefit credit	(27)	(44)		(54)	(195)
Non-U.S. | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	6	8		12	16
Interest cost	15	11		29	23
Expected return on plan assets	(29)	(22)		(58)	(45)
Net periodic benefit credit	$ (8)	$ (3)		$ (17)	$ (6)