Reportable Segment Information - Disaggregation of Revenues by Reportable Segments (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
Retail Services | Operating Segments
Segment Reporting Information [Line Items]
Sales	330	199	869	629
Retail Services | Company operations | Operating Segments
Segment Reporting Information [Line Items]
Sales	234	139	616	421
Retail Services | Non-company operations | Operating Segments
Segment Reporting Information [Line Items]
Sales	96	60	253	208
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 | U.S. Do-It-Yourself (DIY) | Operating Segments
Segment Reporting Information [Line Items]
Sales	162	137	439	407
Global Products | North America installer and other | Operating Segments
Segment Reporting Information [Line Items]
Sales	116	70	316	286
Global Products | International [Member] | Operating Segments
Segment Reporting Information [Line Items]
Sales	$ 184	$ 110	$ 522	$ 379