| **Fair Value Measurements - Summary of Book Value and Principal Amounts of Long-Term Debt (Details) - USD ($) $ in Millions** | 9 Months Ended | 12 Months Ended |
|-------------------------------------------------------------------------------------------------------------------------------|----------------|-----------------|
||
| **Debt Instrument [Line Items]**                                                                                              |           |            |
| Book value                                                                                                                    | $ 790          | $ 789           |
| Principal amount of debt                                                                                                      | $ 793          | $ 793           |
| Senior Debentures 6.900% Due 2028                                                                                             |           |            |
| **Debt Instrument [Line Items]**                                                                                              |           |            |
| Interest rate                                                                                                                 | 6.90%          | 6.90%           |
| Debt issuance year                                                                                                            | 1998           | 1998            |
| Book value                                                                                                                    | $ 27           | $ 27            |
| Principal amount of debt                                                                                                      | $ 28           | $ 28            |
| Senior Debentures 6.920% Due 2028                                                                                             |           |            |
| **Debt Instrument [Line Items]**                                                                                              |           |            |
| Interest rate                                                                                                                 | 6.92%          | 6.92%           |
| Debt issuance year                                                                                                            | 2005           | 2005            |
| Book value                                                                                                                    | $ 391          | $ 391           |
| Principal amount of debt                                                                                                      | $ 391          | $ 391           |
| Senior Notes 6.125% Due 2034                                                                                                  |           |            |
| **Debt Instrument [Line Items]**                                                                                              |           |            |
| Interest rate                                                                                                                 | 6.125%         | 6.125%          |
| Debt issuance year                                                                                                            | 2004           | 2004            |
| Book value                                                                                                                    | $ 372          | $ 371           |
| Principal amount of debt                                                                                                      | $ 374          | $ 374           |

| X                                                                                                                                                                                                                                          |
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+ References
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Face (par) amount of debt instrument at time of issuance.
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| - Definition
Contractual interest rate for funds borrowed, under the debt agreement.
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| - Definition
Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, after deduction of unamortized premium (discount) and debt issuance cost, of long-term debt. Excludes lease obligation.
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