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Stock Incentive Plans - Additional Information (Details) - USD ($) $ in Millions | 3 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Stock-based compensation |  | $ 5 | [1] | $ 6 | [2]
Number of common shares for each converted performance share |  | 1 |  |  |
Stock Appreciation Rights (SARs) [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Unexercised SARs generally lapse expiration period |  | 10 years |  |  |
Grants of share-based payment awards in period |  | 231,000 |  | 300,000 |
Total unrecognized compensation costs |  | $ 7 |  |  |
Model to fair value share-based payment awards |  | Black-Scholes option-pricing model |  |  |
Unrecognized cost expected to be recognized over a weighted-average period (in years) |  | 2 years 2 months 12 days |  |  |
Stock-based compensation |  | $ 2 | [1] | $ 2 | [2]
Stock Appreciation Rights (SARs) [Member] | Minimum [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Vesting period of share-based payment award |  | 1 year |  |  |
Stock Appreciation Rights (SARs) [Member] | Maximum [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Vesting period of share-based payment award |  | 3 years |  |  |
Nonvested Stock Awards [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Grants of share-based payment awards in period |  | 86,000 |  | 81,000 |
Total unrecognized compensation costs |  | $ 10 |  |  |
Unrecognized cost expected to be recognized over a weighted-average period (in years) |  | 2 years 1 month 6 days |  |  |
Stock-based compensation |  | $ 2 | [1] | $ 4 | [2]
Nonvested Stock Awards [Member] | Minimum [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Vesting period of share-based payment award |  | 1 year |  |  |
Nonvested Stock Awards [Member] | Maximum [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Vesting period of share-based payment award |  | 3 years |  |  |
Cash-settled Nonvested Stock Awards [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Vesting period of share-based payment award |  | 3 years |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number |  | 92,000 |  |  |
Stock-based compensation |  | $ 1 |  | 1 |
Restricted Stock [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Stock-based compensation |  | $ 0 |  | $ 1 |
Performance Shares [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Vesting period of share-based payment award |  | 3 years |  |  |
Grants of share-based payment awards in period |  | 51,000 |  | 78,000 |
Total unrecognized compensation costs |  | $ 8 |  |  |
Unrecognized cost expected to be recognized over a weighted-average period (in years) |  | 2 years 6 months |  |  |
Stock-based compensation | [1] | $ 1 |  |  |
[1] | Included $1 million of expense related to cash-settled nonvested restricted stock awards and zero related to cash-settled performance units during the three months ended December 31, 2019
[2] | Included $1 million of expense related to cash-settled nonvested restricted stock awards and $2 million of income related to cash-settled performance units during the three months ended December 31, 2018.

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