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Stockholders' Equity - Additional Information (Detail) - USD ($) | 3 Months Ended |  |
--- | --- | --- | ---
Mar. 31, 2017 | Sep. 30, 2016 | Mar. 31, 2016
Stockholders Equity [Line Items] |  |  |
Shares remaining to be repurchased | 150,000 | 150,000 | 66,276
2016 [Member] |  |  |
Stockholders Equity [Line Items] |  |  |
Implementation of the capital conservation buffer, Percentage | 0.625% |  |
Capital conservation buffer implementation phase-in period | 4 years |  |
2019 [Member] |  |  |
Stockholders Equity [Line Items] |  |  |
Capital Conservation Buffer Maximum Level | 2.50% |  |
Maximum [Member] |  |  |
Stockholders Equity [Line Items] |  |  |
Quantitative limit for trust preferred securities to be included in tier 1 capital | $ 15,000,000,000 |  |

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