Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Sales	$ 983	$ 871	$ 1,872	$ 1,772
Trade receivables, net	553		553		$ 421
U.S.
Disaggregation of Revenue [Line Items]
Sales	514	518	994	1,052
Canada
Disaggregation of Revenue [Line Items]
Sales	14	15	26	29
Mexico
Disaggregation of Revenue [Line Items]
Sales	49	44	90	88
Total North America
Disaggregation of Revenue [Line Items]
Sales	577	577	1,110	1,169
Sweden
Disaggregation of Revenue [Line Items]
Sales	74	63	151	125
Italy
Disaggregation of Revenue [Line Items]
Sales	63	49	121	98
United Kingdom
Disaggregation of Revenue [Line Items]
Sales	39	33	82	68
Other Europe
Disaggregation of Revenue [Line Items]
Sales	38	37	75	75
Total Europe
Disaggregation of Revenue [Line Items]
Sales	214	182	429	366
Brazil
Disaggregation of Revenue [Line Items]
Sales	82	50	138	104
China
Disaggregation of Revenue [Line Items]
Sales	35	26	65	60
India
Disaggregation of Revenue [Line Items]
Sales	50	22	83	45
Other Asia-Pacific
Disaggregation of Revenue [Line Items]
Sales	25	14	47	28
Commercial Truck
Disaggregation of Revenue [Line Items]
Sales	742	598	1,402	1,229
Commercial Truck | U.S.
Disaggregation of Revenue [Line Items]
Sales	337	307	647	635
Commercial Truck | Canada
Disaggregation of Revenue [Line Items]
Sales	0	0	0	0
Commercial Truck | Mexico
Disaggregation of Revenue [Line Items]
Sales	44	39	80	78
Commercial Truck | Total North America
Disaggregation of Revenue [Line Items]
Sales	381	346	727	713
Commercial Truck | Sweden
Disaggregation of Revenue [Line Items]
Sales	74	63	151	125
Commercial Truck | Italy
Disaggregation of Revenue [Line Items]
Sales	58	46	111	91
Commercial Truck | United Kingdom
Disaggregation of Revenue [Line Items]
Sales	36	30	77	63
Commercial Truck | Other Europe
Disaggregation of Revenue [Line Items]
Sales	3	1	5	2
Commercial Truck | Total Europe
Disaggregation of Revenue [Line Items]
Sales	171	140	344	281
Commercial Truck | Brazil
Disaggregation of Revenue [Line Items]
Sales	81	50	137	103
Commercial Truck | China
Disaggregation of Revenue [Line Items]
Sales	34	26	64	60
Commercial Truck | India
Disaggregation of Revenue [Line Items]
Sales	50	22	83	44
Commercial Truck | Other Asia-Pacific
Disaggregation of Revenue [Line Items]
Sales	25	14	47	28
Aftermarket & Industrial
Disaggregation of Revenue [Line Items]
Sales	241	273	470	543
Aftermarket & Industrial | U.S.
Disaggregation of Revenue [Line Items]
Sales	177	211	347	417
Aftermarket & Industrial | Canada
Disaggregation of Revenue [Line Items]
Sales	14	15	26	29
Aftermarket & Industrial | Mexico
Disaggregation of Revenue [Line Items]
Sales	5	5	10	10
Aftermarket & Industrial | Total North America
Disaggregation of Revenue [Line Items]
Sales	196	231	383	456
Aftermarket & Industrial | Sweden
Disaggregation of Revenue [Line Items]
Sales	0	0	0	0
Aftermarket & Industrial | Italy
Disaggregation of Revenue [Line Items]
Sales	5	3	10	7
Aftermarket & Industrial | United Kingdom
Disaggregation of Revenue [Line Items]
Sales	3	3	5	5
Aftermarket & Industrial | Other Europe
Disaggregation of Revenue [Line Items]
Sales	35	36	70	73
Aftermarket & Industrial | Total Europe
Disaggregation of Revenue [Line Items]
Sales	43	42	85	85
Aftermarket & Industrial | Brazil
Disaggregation of Revenue [Line Items]
Sales	1	0	1	1
Aftermarket & Industrial | China
Disaggregation of Revenue [Line Items]
Sales	1	0	1	0
Aftermarket & Industrial | India
Disaggregation of Revenue [Line Items]
Sales	0	0	0	1
Aftermarket & Industrial | Other Asia-Pacific
Disaggregation of Revenue [Line Items]
Sales	$ 0	$ 0	$ 0	$ 0