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Common Stock - Additional Information (Detail) $ / shares in Units, $ in Millions |  | 1 Months Ended | 3 Months Ended | 9 Months Ended |
--- | --- | --- | --- | --- | ---
Oct. 05, 2016 $ / shares shares | Aug. 31, 2016 USD ($) | Sep. 30, 2016 USD ($) | Sep. 30, 2016 USD ($) | Oct. 04, 2016 $ / shares shares
Class of Stock [Line Items] |  |  |  |  |
Reverse stock split ratio |  |  |  | 0.33 |
Decrease in common stock due to reverse stock split |  |  |  | $ (877) |
Increase in additional paid in capital due to reverse stock split |  |  |  | 877 |
Retirement of treasury stock |  | $ 76 |  |  |
Common Stock [Member] |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |
Retirement of treasury stock |  | (76) | $ 76 | 76 |
Additional Capital [Member] |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |
Retirement of treasury stock |  | $ (2,563) | $ 2,563 | $ 2,563 |
Subsequent Event [Member] |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |
Reverse stock split ratio | 0.33 |  |  |  |
Common stock shares outstanding | shares | 400,000,000 |  |  |  | 1,300,000,000
Common stock shares authorized | shares | 600,000,000 |  |  |  | 1,800,000,000
Common stock par value | $ / shares | $ 1.00 |  |  |  | $ 1.00

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