SUPPLEMENTAL PARENT AND GUARANTOR CONDENSED CONSOLIDATING FINANCIAL STATEMENTS - Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Condensed Cash Flow Statements, Captions [Line Items]
CASH PROVIDED BY OPERATING ACTIVITIES	$ 256	$ 251	$ 176
INVESTING ACTIVITIES
Capital expenditures	(103)	(104)	(95)
Cash paid for investment in Transportation Power, Inc.	(6)	(6)	0
Cash paid for business acquisitions, net of cash acquired	(168)	(35)	(34)
Proceeds from sale of equity method investment	0	250	0
Other investing activities	6	6	0
Net investing cash flows provided by discontinued operations	0	0	2
CASH PROVIDED BY (USED FOR) INVESTING ACTIVITIES	(271)	111	(127)
FINANCING ACTIVITIES
Securitization	(38)	(43)	89
Proceeds from debt issuance	0	0	325
Redemption of notes	(24)	(181)	(103)
Repayment of notes and term loan	0	0	(408)
Term loan borrowings	175	0	0
Intercompany advances	0	0	0
Repurchase of common stock	(96)	(100)	0
Deferred issuance costs	(4)	0	0
Debt issuance costs	0	0	(12)
Other financing activities	(2)	(5)	(13)
CASH PROVIDED BY (USED FOR) FINANCING ACTIVITIES	11	(329)	(122)
EFFECT OF CHANGES IN CURRENCY EXCHANGE RATES ON CASH AND CASH EQUIVALENTS	(3)	(6)	1
CHANGE IN CASH AND CASH EQUIVALENTS	(7)	27	(72)
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR	115	88	160
CASH AND CASH EQUIVALENTS AT END OF YEAR	108	115	88
Reportable Legal Entities | Parent
Condensed Cash Flow Statements, Captions [Line Items]
CASH PROVIDED BY OPERATING ACTIVITIES	91	59	33
INVESTING ACTIVITIES
Capital expenditures	(4)	(10)	(9)
Cash paid for investment in Transportation Power, Inc.	(6)	(6)
Cash paid for business acquisitions, net of cash acquired	(168)	(35)	0
Proceeds from sale of equity method investment		250
Other investing activities	6	4
Net investing cash flows provided by discontinued operations			0
CASH PROVIDED BY (USED FOR) INVESTING ACTIVITIES	(172)	203	(9)
FINANCING ACTIVITIES
Securitization	0	0	0
Proceeds from debt issuance			325
Redemption of notes	(24)	(181)	(103)
Repayment of notes and term loan			(408)
Term loan borrowings	175
Intercompany advances	11	35	95
Repurchase of common stock	(96)	(100)
Deferred issuance costs	(4)
Debt issuance costs			(12)
Other financing activities	(1)	(2)	(1)
CASH PROVIDED BY (USED FOR) FINANCING ACTIVITIES	61	(248)	(104)
EFFECT OF CHANGES IN CURRENCY EXCHANGE RATES ON CASH AND CASH EQUIVALENTS	0	0	0
CHANGE IN CASH AND CASH EQUIVALENTS	(20)	14	(80)
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR	24	10	90
CASH AND CASH EQUIVALENTS AT END OF YEAR	4	24	10
Reportable Legal Entities | Guarantors
Condensed Cash Flow Statements, Captions [Line Items]
CASH PROVIDED BY OPERATING ACTIVITIES	49	55	85
INVESTING ACTIVITIES
Capital expenditures	(50)	(49)	(51)
Cash paid for investment in Transportation Power, Inc.	0	0
Cash paid for business acquisitions, net of cash acquired	0	0	(32)
Proceeds from sale of equity method investment		0
Other investing activities	0	0
Net investing cash flows provided by discontinued operations			2
CASH PROVIDED BY (USED FOR) INVESTING ACTIVITIES	(50)	(49)	(81)
FINANCING ACTIVITIES
Securitization	0	0	0
Proceeds from debt issuance			0
Redemption of notes	0	0	0
Repayment of notes and term loan			0
Term loan borrowings	0
Intercompany advances	0	0	0
Repurchase of common stock	0	0
Deferred issuance costs	0
Debt issuance costs			0
Other financing activities	(1)	(3)	(3)
CASH PROVIDED BY (USED FOR) FINANCING ACTIVITIES	(1)	(3)	(3)
EFFECT OF CHANGES IN CURRENCY EXCHANGE RATES ON CASH AND CASH EQUIVALENTS	0	0	0
CHANGE IN CASH AND CASH EQUIVALENTS	(2)	3	1
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR	6	3	2
CASH AND CASH EQUIVALENTS AT END OF YEAR	4	6	3
Reportable Legal Entities | Non- Guarantors
Condensed Cash Flow Statements, Captions [Line Items]
CASH PROVIDED BY OPERATING ACTIVITIES	116	137	58
INVESTING ACTIVITIES
Capital expenditures	(49)	(45)	(35)
Cash paid for investment in Transportation Power, Inc.	0	0
Cash paid for business acquisitions, net of cash acquired	0	0	(2)
Proceeds from sale of equity method investment		0
Other investing activities	0	2
Net investing cash flows provided by discontinued operations			0
CASH PROVIDED BY (USED FOR) INVESTING ACTIVITIES	(49)	(43)	(37)
FINANCING ACTIVITIES
Securitization	(38)	(43)	89
Proceeds from debt issuance			0
Redemption of notes	0	0	0
Repayment of notes and term loan			0
Term loan borrowings	0
Intercompany advances	(11)	(35)	(95)
Repurchase of common stock	0	0
Deferred issuance costs	0
Debt issuance costs			0
Other financing activities	0	0	(9)
CASH PROVIDED BY (USED FOR) FINANCING ACTIVITIES	(49)	(78)	(15)
EFFECT OF CHANGES IN CURRENCY EXCHANGE RATES ON CASH AND CASH EQUIVALENTS	(3)	(6)	1
CHANGE IN CASH AND CASH EQUIVALENTS	15	10	7
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR	85	75	68
CASH AND CASH EQUIVALENTS AT END OF YEAR	100	85	75
Elims
Condensed Cash Flow Statements, Captions [Line Items]
CASH PROVIDED BY OPERATING ACTIVITIES	0	0	0
INVESTING ACTIVITIES
Capital expenditures	0	0	0
Cash paid for investment in Transportation Power, Inc.	0	0
Cash paid for business acquisitions, net of cash acquired	0	0	0
Proceeds from sale of equity method investment		0
Other investing activities	0	0
Net investing cash flows provided by discontinued operations			0
CASH PROVIDED BY (USED FOR) INVESTING ACTIVITIES	0	0	0
FINANCING ACTIVITIES
Securitization	0	0	0
Proceeds from debt issuance			0
Redemption of notes	0	0	0
Repayment of notes and term loan			0
Term loan borrowings	0
Intercompany advances	0	0	0
Repurchase of common stock	0	0
Deferred issuance costs	0
Debt issuance costs			0
Other financing activities	0	0	0
CASH PROVIDED BY (USED FOR) FINANCING ACTIVITIES	0	0	0
EFFECT OF CHANGES IN CURRENCY EXCHANGE RATES ON CASH AND CASH EQUIVALENTS	0	0	0
CHANGE IN CASH AND CASH EQUIVALENTS	0	0	0
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR	0	0	0
CASH AND CASH EQUIVALENTS AT END OF YEAR	$ 0	$ 0	$ 0