Revenue Recognition - Disaggregation of Revenue by Geographical Market (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Revenue	$ 4,219	$ 4,494	$ 12,605	$ 13,294
Inter-segment elimination
Disaggregation of Revenue [Line Items]
Revenue	(73)	(69)	(204)	(243)
Americas | Operating segments
Disaggregation of Revenue [Line Items]
Revenue	2,010	1,946	5,860	5,673
Americas | Operating segments | United States
Disaggregation of Revenue [Line Items]
Revenue	1,649	1,643	4,894	4,755
Americas | Operating segments | Mexico
Disaggregation of Revenue [Line Items]
Revenue	700	645	2,013	1,925
Americas | Operating segments | Other Americas
Disaggregation of Revenue [Line Items]
Revenue	106	127	330	407
Americas | Regional elimination
Disaggregation of Revenue [Line Items]
Revenue	(445)	(469)	(1,377)	(1,414)
EMEA | Operating segments
Disaggregation of Revenue [Line Items]
Revenue	1,752	1,945	5,170	5,854
EMEA | Operating segments | Germany
Disaggregation of Revenue [Line Items]
Revenue	375	443	1,106	1,382
EMEA | Operating segments | Other EMEA
Disaggregation of Revenue [Line Items]
Revenue	1,885	2,011	5,535	5,999
EMEA | Regional elimination
Disaggregation of Revenue [Line Items]
Revenue	(508)	(509)	(1,471)	(1,527)
Asia | Operating segments
Disaggregation of Revenue [Line Items]
Revenue	530	672	1,779	2,010
Asia | Operating segments | China
Disaggregation of Revenue [Line Items]
Revenue	126	187	410	531
Asia | Operating segments | Other Asia
Disaggregation of Revenue [Line Items]
Revenue	406	486	1,373	1,480
Asia | Regional elimination
Disaggregation of Revenue [Line Items]
Revenue	$ (2)	$ (1)	$ (4)	$ (1)