Stock Incentive Plans - Components of Stock-Based Compensation Expense Included in Continuing Operations (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Mar. 31, 2019	[1]	Mar. 31, 2018	[2]	Mar. 31, 2019	[1]	Mar. 31, 2018	[2]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 10		$ 9		$ 16		$ 20
Stock Appreciation Rights (SARs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	2		2		4		3
Nonvested Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	6		5		10		11
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 2		$ 2		$ 2		$ 6

[1] Included $2 million and $3 million of expense related to cash-settled nonvested restricted stock awards during the three and six months ended March 31, 2019 and $2 million of expense related to cash-settled performance units during the three ended March 31, 2019.

[2] Included $2 million and $4 million of expense related to cash-settled nonvested restricted stock awards and $1 million and $3 million of expense related to cash-settled performance units during the three and six months ended March 31, 2018, respectively.