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Income Taxes - Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits (Detail) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Reconciliation Of Unrecognized Tax Benefits [Line Items]      
Unrecognized tax benefit at beginning of year $ 131 $ 118 $ 58
Additions based on tax positions related to the current year 2 9 1
Additions for tax positions of prior years   13 82
Reductions for tax positions of prior years     (5)
Reductions for lapse of applicable statutes of limitations (5) (9) (18)
Unrecognized tax benefit at end of year $ 128 $ 131 $ 118