Stockholders' Equity - Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Before tax
Unrealized translation loss	$ (9)	$ (5)
Amortization of unrecognized prior service credits included in net income	(3)	0
Total other comprehensive (loss) income	(12)	(5)
Tax expense
Unrealized translation loss	0	1
Amortization of unrecognized prior service credits included in net income	1	0
Total other comprehensive (loss) income	1	1
Net of tax
Unrealized translation loss	(9)	(4)
Amortization of unrecognized prior service credits included in net income	(2)	0
Other comprehensive loss	$ (11)	$ (4)