Equity and Noncontrolling Interests - Changes in AOCI (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	$ 2,189	$ 2,717
Aggregate adjustment for the period, net of tax	74	13
Stockholders' equity, ending balance	2,084	2,724
Accumulated Other Comprehensive Income (Loss)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	(569)	(531)
Stockholders' equity, ending balance	(504)	(518)
Accumulated Foreign Currency Adjustment Attributable to Parent
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	(558)	(523)
Aggregate adjustment for the period, net of tax	50	16
Stockholders' equity, ending balance	(508)	(507)
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	(8)	(7)
Current period changes in fair value, net of tax	17	(3)
Reclassification to income, net of tax	(2)	0
Stockholders' equity, ending balance	7	(10)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	(3)	(1)
Stockholders' equity, ending balance	$ (3)	$ (1)