Contingencies - Summary of environmental reserves (Details) $ in Millions	3 Months Ended
	Dec. 31, 2018 USD ($)
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning balance	$ 17
Payments and other	(1)
Accruals	0
Ending balance	16
Superfund Sites
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning balance	12
Payments and other	(1)
Accruals	0
Ending balance	11
Non-Superfund Sites
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning balance	5
Payments and other	0
Accruals	0
Ending balance	$ 5