Annual report pursuant to Section 13 and 15(d)

Investments in Marketable Securities - Fair Value of Financial Assets and Liabilities Measured on Recurring Basis (Parenthetical) (Detail)

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Investments in Marketable Securities - Fair Value of Financial Assets and Liabilities Measured on Recurring Basis (Parenthetical) (Detail) (U.S. Treasury Notes and Bonds Conventional [Member], USD $)
In Millions, unless otherwise specified
Jan. 31, 2014
U.S. Treasury Notes and Bonds Conventional [Member]
  
Assets And Liabilities Carrying Value And Fair Value [Line Items]  
Investments reclassified from level 1 to level 2 $ 9.1