Goodwill - Additional Information (Details) $ in Millions			9 Months Ended
		Apr. 30, 2018 USD ($)	Jun. 30, 2018 USD ($) unit segment	Sep. 30, 2017 USD ($)
Goodwill [Line Items]
Goodwill from acquisition	[1]		$ 419	$ 414
Number of reportable segments | segment			2
Commercial Truck & Trailer
Goodwill [Line Items]
Number of reporting units | unit			2
Goodwill from acquisition			$ 289	283
Goodwill tax deductible period		15 years
Aftermarket & Industrial
Goodwill [Line Items]
Number of reporting units | unit			3
Goodwill from acquisition			$ 130	$ 131
AA Gear & Manufacturing, Inc.
Goodwill [Line Items]
Purchase price		$ 36
Goodwill from acquisition		$ 9

[1] As of June 30, 2018, Assets and liabilities held for sale consisted of $1 million Net property. As of September 30, 2017, Assets and liabilities held for sale were: (i) $1 million Cash and cash equivalents; (ii) $13 million Receivables, trade and other, net; (iii) $2 million Inventories; (iv) $3 million Net property; (v) $1 million Goodwill; (vi) $1 million Other assets; (vii) $12 million Accounts and notes payable; and (viii) $2 million Noncontrolling interests.