Stock Incentive Plans - Components of Stock-Based Compensation Expense Included in Continuing Operations (Parenthetical) (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Mar. 31, 2020		Mar. 31, 2019		Mar. 31, 2020		Mar. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 4	[1]	$ 10	[2]	$ 9	[1]	$ 16	[2]
Cash-settled Nonvested Restricted Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	0		2		1		$ 3
Cash-settled Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 0		$ 2		$ 0

[1] Included zero million and $1 million of expense related to cash-settled nonvested restricted stock awards during the three and six months ended March 31, 2020 and zero million related to cash-settled performance units during the three and six months ended March 31, 2020

[2] 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 months ended March 31, 2019.