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Fair Value of Financial Investments - Additional Information (Detail) (USD $)
Sep. 30, 2012
Dec. 31, 2011
Aggregate carrying value of remaining private equity funds $ 69,000,000  
Estimated market value of long-term and short-term debt 3,900,000,000 4,000,000,000
Aggregate carrying value of long-term and short-term debt $ 3,600,000,000 $ 4,000,000,000