Income Taxes - Schedule of Components of Net Deferred Tax Assets and Liabilities (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Disclosure [Abstract]
Deferred tax assets, Depreciation	$ 147aa_DeferredTaxAssetsDepreciation	$ 185aa_DeferredTaxAssetsDepreciation
Deferred tax assets, Employee benefits	2,413	2,499
Deferred tax assets, Loss provisions	441	437
Deferred tax assets, Deferred income/expense	30us-gaap_DeferredTaxAssetsDeferredIncome	87us-gaap_DeferredTaxAssetsDeferredIncome
Deferred tax assets, Tax loss carryforwards	2,075	2,229
Deferred tax assets, Tax credit carryforwards	625	567
Deferred tax assets, Derivatives and hedging activities	5	74
Deferred tax assets, Other	521us-gaap_DeferredTaxAssetsOther	310us-gaap_DeferredTaxAssetsOther
Deferred tax assets, Gross	6,257us-gaap_DeferredTaxAssetsGross	6,388us-gaap_DeferredTaxAssetsGross
Deferred tax assets, Valuation allowance	(1,668)	(1,804)	(1,400)	(1,398)
Deferred tax assets, net	4,589us-gaap_DeferredTaxAssetsNet	4,584us-gaap_DeferredTaxAssetsNet
Deferred tax liabilities, Depreciation	1,187aa_DeferredTaxLiabilitiesDepreciation	1,150aa_DeferredTaxLiabilitiesDepreciation
Deferred tax liabilities, Employee benefits	37	36
Deferred tax liabilities, Loss provisions	10aa_DeferredTaxLiabilitiesLossProvisions	14aa_DeferredTaxLiabilitiesLossProvisions
Deferred tax liabilities, Deferred income/expense	230	188
Deferred tax liabilities, Tax loss carryforwards	0	0
Deferred tax liabilities, Tax credit carryforwards	0	0
Deferred tax liabilities, Derivatives and hedging activities	39	25
Deferred tax liabilities, Other	297us-gaap_DeferredTaxLiabilitiesOther	261us-gaap_DeferredTaxLiabilitiesOther
Deferred tax liabilities, Gross	1,800aa_DeferredTaxLiabilitiesGross	1,674aa_DeferredTaxLiabilitiesGross
Deferred tax liabilities, Valuation allowance	0	0
Deferred tax liabilities, Net	$ 1,800us-gaap_DeferredTaxLiabilities	$ 1,674us-gaap_DeferredTaxLiabilities

Deferred tax assets, depreciation.

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Deferred tax assets, derivatives and hedging activities.

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Deferred tax liabilities depreciation.

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Deferred tax liabilities, derivatives and hedging activities.

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Deferred tax liabilities, employee benefits.

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- Definition

Deferred tax liabilities gross.

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- Definition

Deferred tax liabilities, loss provisions.

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- Definition

Deferred tax liabilities, tax credit carryforwards.

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- Definition

Deferred tax liabilities, tax loss carryforwards.

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Deferred tax liabilities valuation allowance.

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- Definition

Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from deferred income.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards.

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-Glossary Deferred Tax Asset

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Amount after allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards.

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- Definition

Amount before allocation of valuation allowances of deferred tax asset attributable to deductible operating loss carryforwards.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences not separately disclosed.

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- Definition

The tax effect as of the balance sheet date of the amount of future tax deductions arising from all unused tax credit carryforwards which have been reduced by a valuation allowance.

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-Glossary Carryforwards

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The tax effect as of the balance sheet date of the amount of the estimated future tax deductions arising from employee benefit costs not otherwise specified in the taxonomy, which can only be deducted for tax purposes when actual costs are incurred, and which can only be realized if sufficient tax-basis income is generated in future periods to enable the deduction to be taken.

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- Definition

Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from loss reserves other than estimated credit losses.

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- Definition

Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

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- Definition

Amount of deferred tax liability attributable to taxable temporary differences net of deferred tax asset attributable to deductible temporary differences and carryforwards after valuation allowances.

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Amount of deferred tax liability attributable to taxable temporary differences from capitalized costs.

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Amount of deferred tax liability attributable to taxable temporary differences not separately disclosed.

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