Fair Value Measurements - Schedule of Assets and Liabilities at Fair Value (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Millions	Mar. 31, 2018	Sep. 30, 2017
Assets
Cash equivalents	$ 31	$ 46
Foreign currency derivatives	1	1
Non-qualified trust funds	28	30
Total assets at fair value	60	77
Liabilities
Foreign currency derivatives	1	1
Total liabilities at fair value	1	1
Quoted prices in active markets for identical assets, Level 1
Assets
Cash equivalents	31	46
Foreign currency derivatives	1	1
Non-qualified trust funds	28	30
Total assets at fair value	60	77
Liabilities
Foreign currency derivatives	1	1
Total liabilities at fair value	1	$ 1
Other Current Assets
Assets
Non-qualified trust funds	$ 2