Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Sales	$ 871	$ 1,156	$ 1,772	$ 2,194
Trade receivables, net	435		435		$ 517
U.S.
Disaggregation of Revenue [Line Items]
Sales	517	676	1,052	1,266
Canada
Disaggregation of Revenue [Line Items]
Sales	15	17	29	35
Mexico
Disaggregation of Revenue [Line Items]
Sales	45	63	88	120
Total North America
Disaggregation of Revenue [Line Items]
Sales	577	756	1,169	1,421
Sweden
Disaggregation of Revenue [Line Items]
Sales	63	74	125	148
Italy
Disaggregation of Revenue [Line Items]
Sales	49	64	98	125
United Kingdom
Disaggregation of Revenue [Line Items]
Sales	33	47	68	91
Other Europe
Disaggregation of Revenue [Line Items]
Sales	37	22	75	44
Total Europe
Disaggregation of Revenue [Line Items]
Sales	182	207	366	408
Brazil
Disaggregation of Revenue [Line Items]
Sales	50	63	104	113
China
Disaggregation of Revenue [Line Items]
Sales	26	44	60	85
India
Disaggregation of Revenue [Line Items]
Sales	22	62	45	119
Other Asia-Pacific
Disaggregation of Revenue [Line Items]
Sales	14	24	28	48
Commercial Truck
Disaggregation of Revenue [Line Items]
Sales	557	837	1,147	1,581
Commercial Truck | U.S.
Disaggregation of Revenue [Line Items]
Sales	269	413	561	763
Commercial Truck | Canada
Disaggregation of Revenue [Line Items]
Sales	0	0	0	0
Commercial Truck | Mexico
Disaggregation of Revenue [Line Items]
Sales	36	50	70	97
Commercial Truck | Total North America
Disaggregation of Revenue [Line Items]
Sales	305	463	631	860
Commercial Truck | Sweden
Disaggregation of Revenue [Line Items]
Sales	63	74	125	148
Commercial Truck | Italy
Disaggregation of Revenue [Line Items]
Sales	46	59	91	116
Commercial Truck | United Kingdom
Disaggregation of Revenue [Line Items]
Sales	30	45	63	86
Commercial Truck | Other Europe
Disaggregation of Revenue [Line Items]
Sales	1	3	2	6
Commercial Truck | Total Europe
Disaggregation of Revenue [Line Items]
Sales	140	181	281	356
Commercial Truck | Brazil
Disaggregation of Revenue [Line Items]
Sales	50	63	103	113
Commercial Truck | China
Disaggregation of Revenue [Line Items]
Sales	26	44	60	85
Commercial Truck | India
Disaggregation of Revenue [Line Items]
Sales	22	62	44	119
Commercial Truck | Other Asia-Pacific
Disaggregation of Revenue [Line Items]
Sales	14	24	28	48
Aftermarket, Industrial and Trailer
Disaggregation of Revenue [Line Items]
Sales	314	319	625	613
Aftermarket, Industrial and Trailer | U.S.
Disaggregation of Revenue [Line Items]
Sales	248	263	491	503
Aftermarket, Industrial and Trailer | Canada
Disaggregation of Revenue [Line Items]
Sales	15	17	29	35
Aftermarket, Industrial and Trailer | Mexico
Disaggregation of Revenue [Line Items]
Sales	9	13	18	23
Aftermarket, Industrial and Trailer | Total North America
Disaggregation of Revenue [Line Items]
Sales	272	293	538	561
Aftermarket, Industrial and Trailer | Sweden
Disaggregation of Revenue [Line Items]
Sales	0	0	0	0
Aftermarket, Industrial and Trailer | Italy
Disaggregation of Revenue [Line Items]
Sales	3	5	7	9
Aftermarket, Industrial and Trailer | United Kingdom
Disaggregation of Revenue [Line Items]
Sales	3	2	5	5
Aftermarket, Industrial and Trailer | Other Europe
Disaggregation of Revenue [Line Items]
Sales	36	19	73	38
Aftermarket, Industrial and Trailer | Total Europe
Disaggregation of Revenue [Line Items]
Sales	42	26	85	52
Aftermarket, Industrial and Trailer | Brazil
Disaggregation of Revenue [Line Items]
Sales	0	0	1	0
Aftermarket, Industrial and Trailer | China
Disaggregation of Revenue [Line Items]
Sales	0	0	0	0
Aftermarket, Industrial and Trailer | India
Disaggregation of Revenue [Line Items]
Sales	0	0	1	0
Aftermarket, Industrial and Trailer | Other Asia-Pacific
Disaggregation of Revenue [Line Items]
Sales	$ 0	$ 0	$ 0	$ 0