Impairment and Restructuring Charges (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended		12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2018	Sep. 30, 2018
Restructuring and asset impairment charges
Restructuring charges		$ 7		$ 23	$ 15
Other net restructuring charges		3
Other restructuring charges including refinement of prior year restructuring activities				1
Finance transformation initiative in North America
Restructuring and asset impairment charges
Restructuring charges		4		5
Employee Severance related costs
Restructuring accrual
Balance in severance accrual at December 31, 2016	$ 11			7
Payments made to terminated employees				(14)
Balance in severance accrual at September 30, 2017		11		11
Employee Severance related costs | Forecast
Restructuring and asset impairment charges
Severance accrual expected to be paid within next twelve months							$ 9
Employee Severance related costs | Argentina employee-related severance
Restructuring accrual
Restructuring charge for employee-related severance costs				15
Employee Severance related costs | Finance transformation initiative in North America
Restructuring and asset impairment charges
Restructuring charges		3		3
Restructuring accrual
Restructuring charge for employee-related severance costs				3
Employee Severance related costs | Other employee-related severance
Restructuring accrual
Restructuring charge for employee-related severance costs				2
Employee Severance related costs | Prior year restructuring activities
Restructuring accrual
Restructuring charge for employee-related severance costs				(2)
Employee Severance related costs | South America employee-related severance
Restructuring and asset impairment charges
Restructuring charges					3
Non employee severance costs | Finance transformation initiative in North America
Restructuring and asset impairment charges
Restructuring charges		$ 1		2
Employee Severance And Other Costs | Argentina employee-related severance
Restructuring and asset impairment charges
Restructuring charges				$ 17
Employee Severance And Other Costs | Finance transformation initiative in North America | Minimum | Forecast
Restructuring and asset impairment charges
Restructuring charges	3					$ 1
Employee Severance And Other Costs | Finance transformation initiative in North America | Maximum | Forecast
Restructuring and asset impairment charges
Restructuring charges	$ 5					$ 2
Employee Severance And Other Costs | IT transformation
Restructuring and asset impairment charges
Restructuring charges			$ 2		10
Facility Closing | Port Colborne Ontario Canada Plant
Restructuring and asset impairment charges
Restructuring charges					$ 2