Contingencies - Additional Information (Details) $ in Millions	6 Months Ended	12 Months Ended
	Mar. 31, 2021 USD ($) site	Sep. 30, 2020 USD ($) claim
Loss Contingencies [Line Items]
Environmental accrual balance	$ 14	$ 16
Discounted amount environmental accrual for on-going operations maintenance and monitoring	13
Undiscounted amount environmental accrual for on-going operations maintenance and monitoring	$ 14
Rockwell Asbestos
Loss Contingencies [Line Items]
Number of pending claims | claim		1,200
Obligation period for asbestos personal injury claims	38 years	38 years
Pending and future claims	$ 75
Asbestos-related insurance recoveries	$ 59	$ 62
Low Range
Loss Contingencies [Line Items]
Site contingency, accrual, discount rate	0.00%
Low Range | Rockwell Asbestos
Loss Contingencies [Line Items]
Possible loss		78
High Range
Loss Contingencies [Line Items]
Site contingency, accrual, discount rate	1.50%
Superfund Sites
Loss Contingencies [Line Items]
Number of superfund environmental sites | site	10
Environmental costs reasonably possible	$ 22
Environmental accrual balance	10	11
Non-Superfund Sites
Loss Contingencies [Line Items]
Environmental costs reasonably possible	13
Environmental accrual balance	$ 4	$ 5