Equity Items - Components of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Equity [Abstract]
Unrealized translation gain (loss), before tax	$ 38	$ (31)
Unrealized translation gain (loss), net of tax	38	(31)
Adjustment of unrecognized prior service cost (credit), before tax		(7)
Adjustment of unrecognized prior service cost (credit), tax		1
Adjustment of unrecognized prior service cost (credit), net of tax		(6)
Total other comprehensive income (loss), before tax	38	(38)
Total other comprehensive income (loss), tax		1
Other comprehensive income (loss)	$ 38	$ (37)