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Securities - Additional Information (Detail) (USD $) | 3 Months Ended |  |
--- | --- | --- | ---
Mar. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Schedule Of Marketable Securities [Line Items] |  |  |
Percentage of municipal bond portfolio issued by political subdivision or agencies within the state of Texas | 96.70% |  |
Percentage of municipal bond portfolio issued by political subdivision or agencies within the state of Texas guaranteed by Texas permanent school fund | 68.80% |  |
Carrying value of pledged securities | $ 2,600,000,000 | $ 3,000,000,000 |
Available for Sale, Estimated Fair Value | 5,482,465,000 | 5,895,436,000 |
Available for sale securities reclassified to held to maturity, unrealized gain |  |  | 165,700,000
Available for sale securities reclassified to held to maturity, unrealized gain net of tax |  |  | 107,700,000
Net unamortized unrealized gain on transferred securities included in accumulated other comprehensive income Pre Tax | 120,200,000 |  |
Net unamortized unrealized gain on transferred securities included in accumulated other comprehensive income, net of tax | 78,100,000 |  |
Reclassified To Held To Maturity [Member] |  |  |
Schedule Of Marketable Securities [Line Items] |  |  |
Available for Sale, Estimated Fair Value |  |  | $ 2,300,000,000

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