Fair Value Disclosures - Financial Assets and Liabilities Accounted for at Fair Value on Recurring Basis (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Feb. 28, 2013	Nov. 30, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. government securities, fair value	$ 357.2	$ 404.3