Stock Incentive Plans - Components of Pretax Compensation Expense for Stock-Based Awards (Net of Forfeitures) and Associated Income Tax Benefits (Parenthetical) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2022		Sep. 30, 2021		Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 24	[1]	$ 18	[2]	$ 16	[3]
Cash-settled Nonvested Restricted Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	4		3		2
Cash-settled Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 2		$ 0		$ 0

[1] The year ended September 30, 2022 included $4 million and $2 million of expense related to cash-settled nonvested restricted stock awards and cash-settled performance units, respectively.

[2] The year ended September 30, 2021 included $3 million and zero of expense related to cash-settled nonvested restricted stock awards and cash-settled performance units, respectively.

[3] The year ended September 30, 2020 included $2 million and zero of expense related to cash-settled nonvested restricted stock awards and cash-settled performance units, respectively.