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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, 2011
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Income Tax Disclosure [Abstract]          
Tax depreciation greater (less) than book depreciation     $ (23) $ 13 $ 51
Book amortization less than (in excess of) tax amortization     (57) 16 0
Liabilities currently not deductible for tax     (48) (29) (28)
Net tax losses (benefited) utilized     50 (11) (37)
Change in valuation allowance on deferred tax assets (89) (78) (21) (89) (78)
Net tax credits utilized     2 53 24
Other     (3) 1 (8)
Deferred income tax, Total     $ (100) $ (46) $ (76)