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Income Taxes - Income Tax Expense (Benefit) Table (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]    
Income tax expense (benefit) $ 456 $ 352
Effective tax rate 49.00% 14.00%