Derivative Financial Instruments - Remaining Contract Maturity of Fair Value of OTC Derivative Assets and Liabilities (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	May 31, 2014
Fair Value Disclosures [Abstract]
Exchange traded derivative assets	$ 11.6
Cash collateral received	143.0
Exchange traded derivative liabilities, with fair value	22.2
Cash collateral pledged	$ 241.6