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Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions | 6 Months Ended |  |
--- | --- | --- | ---
Mar. 31, 2016 | Mar. 31, 2015 | Jan. 31, 2015 | Sep. 30, 2007
Class Of Stock [Line Items] |  |  |  |
Repurchase authorization, shares |  |  | 5,000,000 | 10,000,000
Cash dividends paid to common stockholders | $ 28 | $ 28 |  |
Cash dividend paid per share | $ 0.44 | $ 0.44 |  |
Noncontrolling interest dividends declared | $ 16 | $ 13 |  |
Cash dividends paid to noncontrolling interests | $ 3 | $ 11 |  |
2007 Share Repurchase Authorization [Member] |  |  |  |
Class Of Stock [Line Items] |  |  |  |
Common stock shares repurchased |  | 925,700 |  |
January 2015 Share Repurchase Authorization [Member] |  |  |  |
Class Of Stock [Line Items] |  |  |  |
Common stock shares repurchased | 1,700,676 |  |  |
Shares remaining available for repurchase under the current authorization | 3,299,324 |  |  |

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