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Stock-Based Compensation (Details) $ in Millions		12 Months Ended
Stock-Based Compensation (Details) $ in Millions	Oct. 31, 2016	Sep. 30, 2019 USD ($) shares	Sep. 30, 2018 USD ($) shares	Sep. 30, 2017 USD ($) shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation		$ 20	$ 47	$ 45
Income tax benefit recognized for share-based compensation arrangements		$ 0	$ 0	$ 21
Conversion ratio (in shares)	0.1
Stock options granted (in shares) \| shares		0	0	0
Option exercised in period, intrinsic value		$ 5	$ 7	$ 18
Payments made in conjunction with exercise of SARs		$ 4
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		3 years
Unrecognized compensation related to unvested share arrangements		$ 11
Recognition period for unrecognized compensation cost		1 year 9 months 18 days
Performance Shares (PSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation related to unvested share arrangements		$ 3
Recognition period for unrecognized compensation cost		1 year 7 months 6 days
Performance period		3 years
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period		10 years
Stock Options \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		2 years
Stock Options \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		3 years
Stock Appreciation Rights (SARs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Payments made in conjunction with exercise of SARs		$ 1	$ 3	$ 1