Reportable Segment Information - Disaggregation of Revenues by Geographical Market (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Segment Reporting Information [Line Items]
Sales	$ 792	$ 516	$ 2,146	$ 1,701
Operating Segments
Segment Reporting Information [Line Items]
Sales	792	516	2,146	1,701
North America
Segment Reporting Information [Line Items]
Sales	608	406	1,624	1,322
Retail Services | Operating Segments
Segment Reporting Information [Line Items]
Sales	330	199	869	629
Retail Services | Operating Segments | Company operations
Segment Reporting Information [Line Items]
Sales	234	139	616	421
Retail Services | North America
Segment Reporting Information [Line Items]
Sales	330	199	869	629
Retail Services | EMEA
Segment Reporting Information [Line Items]
Sales	0	0	0	0
Retail Services | Asia Pacific
Segment Reporting Information [Line Items]
Sales	0	0	0	0
Retail Services | Latin America
Segment Reporting Information [Line Items]
Sales	0	0	0	0
Global Products
Segment Reporting Information [Line Items]
Sales	462	317	1,277	1,072
Global Products | Operating Segments
Segment Reporting Information [Line Items]
Sales	462	317	1,277	1,072
Global Products | Operating Segments | North America installer and other
Segment Reporting Information [Line Items]
Sales	116	70	316	286
Global Products | Operating Segments | International [Member]
Segment Reporting Information [Line Items]
Sales	184	110	522	379
Global Products | North America
Segment Reporting Information [Line Items]
Sales	278	207	755	693
Global Products | EMEA
Segment Reporting Information [Line Items]
Sales	56	34	161	125
Global Products | Asia Pacific
Segment Reporting Information [Line Items]
Sales	96	65	267	193
Global Products | Latin America
Segment Reporting Information [Line Items]
Sales	$ 32	$ 11	$ 94	$ 61