Supplemental Guarantor Condensed Consolidating Financial Statements - Condensed Consolidating Statement of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Condensed Cash Flow Statements, Captions [Line Items]
CASH PROVIDED BY (USED FOR) OPERATING ACTIVITIES	$ 11	$ 33
INVESTING ACTIVITIES
Capital expenditures	(23)	(18)
Proceeds from sale of equity method investment	0	250
Cash paid for investment in Transportation Power, Inc.	(3)	(3)
Other investing activities	(1)	0
CASH PROVIDED BY (USED FOR) INVESTING ACTIVITIES	(27)	229
FINANCING ACTIVITIES
Borrowings and securitization	78	(51)
Redemption of notes	0	(181)
Repurchase of common stock	(50)	0
Intercompany advances	0	0
Other financing activities	(1)	(1)
CASH PROVIDED BY (USED FOR) FINANCING ACTIVITIES	27	(233)
EFFECT OF CHANGES IN FOREIGN CURRENCY EXCHANGE RATES ON CASH AND CASH EQUIVALENTS	1	(1)
CHANGE IN CASH AND CASH EQUIVALENTS	12	28
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	115	88
CASH AND CASH EQUIVALENTS AT END OF PERIOD	127	116
Elims
Condensed Cash Flow Statements, Captions [Line Items]
CASH PROVIDED BY (USED FOR) OPERATING ACTIVITIES	0	0
INVESTING ACTIVITIES
Capital expenditures	0	0
Proceeds from sale of equity method investment		0
Cash paid for investment in Transportation Power, Inc.	0	0
CASH PROVIDED BY (USED FOR) INVESTING ACTIVITIES	0	0
FINANCING ACTIVITIES
Borrowings and securitization	0	0
Redemption of notes		0
Repurchase of common stock	0
Intercompany advances	0	0
Other financing activities	0	0
CASH PROVIDED BY (USED FOR) FINANCING ACTIVITIES	0	0
EFFECT OF CHANGES IN FOREIGN CURRENCY EXCHANGE RATES ON CASH AND CASH EQUIVALENTS	0	0
CHANGE IN CASH AND CASH EQUIVALENTS	0	0
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	0	0
CASH AND CASH EQUIVALENTS AT END OF PERIOD	0	0
Parent | Reportable Legal Entities
Condensed Cash Flow Statements, Captions [Line Items]
CASH PROVIDED BY (USED FOR) OPERATING ACTIVITIES	(9)	(75)
INVESTING ACTIVITIES
Capital expenditures	(1)	(1)
Proceeds from sale of equity method investment		250
Cash paid for investment in Transportation Power, Inc.	(3)	(3)
Other investing activities	0
CASH PROVIDED BY (USED FOR) INVESTING ACTIVITIES	(4)	246
FINANCING ACTIVITIES
Borrowings and securitization	45	0
Redemption of notes		(181)
Repurchase of common stock	(50)
Intercompany advances	18	23
Other financing activities	0	0
CASH PROVIDED BY (USED FOR) FINANCING ACTIVITIES	13	(158)
EFFECT OF CHANGES IN FOREIGN CURRENCY EXCHANGE RATES ON CASH AND CASH EQUIVALENTS	0	0
CHANGE IN CASH AND CASH EQUIVALENTS	0	13
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	24	10
CASH AND CASH EQUIVALENTS AT END OF PERIOD	24	23
Guarantors | Reportable Legal Entities
Condensed Cash Flow Statements, Captions [Line Items]
CASH PROVIDED BY (USED FOR) OPERATING ACTIVITIES	15	10
INVESTING ACTIVITIES
Capital expenditures	(12)	(9)
Proceeds from sale of equity method investment		0
Cash paid for investment in Transportation Power, Inc.	0	0
Other investing activities	0
CASH PROVIDED BY (USED FOR) INVESTING ACTIVITIES	(12)	(9)
FINANCING ACTIVITIES
Borrowings and securitization	0	0
Redemption of notes		0
Repurchase of common stock	0
Intercompany advances	0	0
Other financing activities	(1)	(1)
CASH PROVIDED BY (USED FOR) FINANCING ACTIVITIES	(1)	(1)
EFFECT OF CHANGES IN FOREIGN CURRENCY EXCHANGE RATES ON CASH AND CASH EQUIVALENTS	0	0
CHANGE IN CASH AND CASH EQUIVALENTS	2	0
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	6	3
CASH AND CASH EQUIVALENTS AT END OF PERIOD	8	3
Non- Guarantors | Reportable Legal Entities
Condensed Cash Flow Statements, Captions [Line Items]
CASH PROVIDED BY (USED FOR) OPERATING ACTIVITIES	5	98
INVESTING ACTIVITIES
Capital expenditures	(10)	(8)
Proceeds from sale of equity method investment		0
Cash paid for investment in Transportation Power, Inc.	0	0
Other investing activities	(1)
CASH PROVIDED BY (USED FOR) INVESTING ACTIVITIES	(11)	(8)
FINANCING ACTIVITIES
Borrowings and securitization	33	(51)
Redemption of notes		0
Repurchase of common stock	0
Intercompany advances	(18)	(23)
Other financing activities	0	0
CASH PROVIDED BY (USED FOR) FINANCING ACTIVITIES	15	(74)
EFFECT OF CHANGES IN FOREIGN CURRENCY EXCHANGE RATES ON CASH AND CASH EQUIVALENTS	1	(1)
CHANGE IN CASH AND CASH EQUIVALENTS	10	15
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	85	75
CASH AND CASH EQUIVALENTS AT END OF PERIOD	$ 95	$ 90