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Income Taxes - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended 9 Months Ended
Sep. 30, 2012
Sep. 30, 2011
Sep. 30, 2012
Sep. 30, 2011
Income Tax Expense (Benefit) $ 551 $ 45 $ 710 $ 136
Effective Income Tax Rate, Continuing Operations 34.00% 17.00% 31.00% 19.00%