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Income Taxes - Summary of Deferred Tax Assets and Liabilities (Detail) (USD $) In Millions, unless otherwise specified | Dec. 31, 2012 | Dec. 31, 2011
--- | --- | ---
Income Taxes [Line Items] |  |
Tax benefit of loss carryforwards | $ 628 | $ 527
Liabilities currently not deductible for tax | 263 | 219
Tax credit carryforwards | 35 | 73
Unrealized loss on cash flow hedges and retirement liabilities | 48 | 51
Deferred tax assets, Gross, Total | 974 | 870
Valuation allowance against tax benefit of loss carryforwards | (504) | (454)
Other valuation allowance | (45) | (103)
Deferred Tax Assets, Net, Total | 425 | 313
Tax depreciation in excess of book depreciation | 199 | 135
Other assets book value in excess of tax value | 77 | 20
Unrealized gain on cash flow hedges and retirement liabilities | 19 | 8
Other | 30 | 0
Deferred tax liabilities, total | 325 | 163
Net deferred tax assets | $ 100 | $ 150

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