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Income Taxes - Summary of Deferred Income Taxes Provided on Temporary Differences (Detail) (USD $)
In Millions, unless otherwise specified
 3 Months Ended 12 Months Ended
Dec. 31, 2012
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Income Taxes [Line Items]        
Tax depreciation greater (less) than book depreciation   $ 13 $ 51 $ (13)
Book amortization less than (in excess of) tax amortization   16   (20)
Liabilities currently not deductible for tax   (29) (28) (27)
Net tax losses (benefited) utilized   (11) (37) 48
Change in valuation allowance on deferred tax assets (89) (89) (78) (3)
Net tax credits utilized   53 24 0
Other   1 (8) (2)
Deferred income tax, Total   $ (46) $ (76) $ (17)