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Income Taxes - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Jun. 30, 2012
Jun. 30, 2011
Income Taxes [Line Items]        
Provision for income tax $ 180 $ 169 $ 352 $ 281
Effective tax rate 31.80% 33.30% 30.20% 31.80%