Use of Derivative Financial Instruments, Offsetting Disclosure and Changes in Other Comprehensive Income by Component - Offsetting Disclosures for All Derivatives Held and Repurchase Arrangements and Similar Borrowings Outstanding (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Interest Rate Swap agreements [Member]
Derivative Instruments And Hedging Activities [Line Items]
Accrued interest	$ 6.1	$ 7.8
Repurchase Arrangements and Similar Borrowings [Member]
Derivative Instruments And Hedging Activities [Line Items]
Accrued interest	$ 2.8	$ 7.0