| **Fair Value Measurements - Summary of Book Value and Principal Amounts of Long-Term Debt (Detail) - USD ($) $ in Millions** | 3 Months Ended | 12 Months Ended |
|------------------------------------------------------------------------------------------------------------------------------|----------------|-----------------|
||
| **Debt Instrument [Line Items]**                                                                                             |           |            |
| Book value                                                                                                                   | $ 786          | $ 786           |
| 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                                                                                                                   | $ 26           | $ 26            |
| 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 6.152% Due 2034                                                                                                 |           |            |
| **Debt Instrument [Line Items]**                                                                                             |           |            |
| Interest rate                                                                                                                | 6.125%         | 6.125%          |
| Debt issuance year                                                                                                           | 2004           | 2004            |
| Book value                                                                                                                   | $ 369          | $ 369           |
| Principal amount of debt                                                                                                     | $ 374          | $ 374           |

| X                                                                                                                                                                                                                                          |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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Debt instrument issuance year.
+ References
No definition available.
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|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Face (par) amount of debt instrument at time of issuance.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Contractual interest rate for funds borrowed, under the debt agreement.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                               |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - 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.
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.
+ References
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| X                                                                                                                                                                                     |
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| X                                                                                                                                                                                        |
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| X                                                                                                                                                                                     |
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