Equity and Noncontrolling Interests - Changes in AOCI (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	$ 2,717	$ 4,592
Aggregate adjustment for the period, net of tax	13	66
Balance at end of period	2,724	4,429
Accumulated other comprehensive income (loss), end of period
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(531)	(397)
Balance at end of period	(518)	(336)
Foreign currency translation adjustments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(523)	(398)
Aggregate adjustment for the period, net of tax	16	71
Balance at end of period	(507)	(327)
Realized and unrealized gains (losses) on derivatives
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(7)	3
Current period changes in fair value, net of tax	(3)	(9)
Reclassification to income, net of tax	0	(1)
Balance at end of period	(10)	(7)
Pension and postretirement plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(1)	(2)
Balance at end of period	$ (1)	$ (2)