Contingencies - Additional Information (Details) $ in Millions		6 Months Ended		12 Months Ended
	Jan. 22, 2019 USD ($)	Mar. 31, 2020 USD ($) site claim	Mar. 31, 2019 USD ($)	Sep. 30, 2019 USD ($) claim
Loss Contingencies [Line Items]
Environmental accrual balance		$ 13		$ 15
Discounted amount environmental accrual for on-going operations maintenance and monitoring		13
Undiscounted amount environmental accrual for on-going operations maintenance and monitoring		15
Asbestos related liability remeasurement		$ 0	$ 31
Low Range
Loss Contingencies [Line Items]
Site contingency, accrual, discount rate		1.50%
High Range
Loss Contingencies [Line Items]
Site contingency, accrual, discount rate		2.25%
Maremont Asbestos
Loss Contingencies [Line Items]
Damages sought	$ 51
Asbestos related liability remeasurement	$ 31		$ 31
Obligation period for asbestos personal injury claims				40 years
Rockwell Asbestos
Loss Contingencies [Line Items]
Number of pending claims | claim		1,400		1,400
Pending and future claims		$ 87		$ 91
Asbestos-related insurance recoveries		$ 60		61
Rockwell Asbestos | Low Range
Loss Contingencies [Line Items]
Possible loss				91
Rockwell Asbestos | High Range
Loss Contingencies [Line Items]
Possible loss				181
Superfund Sites
Loss Contingencies [Line Items]
Number of Superfund environmental sites | site		10
Environmental costs reasonably possible		$ 23
Environmental accrual balance		9		11
Non-Superfund Sites
Loss Contingencies [Line Items]
Environmental costs reasonably possible		13
Environmental accrual balance		$ 4		$ 4