Income Taxes - Schedule of Components of Net Deferred Tax Assets and Liabilities (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Deferred Tax Assets And Liabilities [Line Items]
Deferred tax assets, Depreciation	$ 104	$ 74
Deferred tax assets, Employee benefits	2,742	2,668
Deferred tax assets, Loss provisions	368	325
Deferred tax assets, Deferred income/expense	53	45
Deferred tax assets, Tax loss carryforwards	2,186	2,035
Deferred tax assets, Tax credit carryforwards	508	477
Deferred tax assets, Derivatives and hedging activities	117	109
Deferred tax assets, Other	324	315
Deferred tax assets, Gross	6,402	6,048
Deferred tax assets, Valuation allowance	(1,400)	(1,398)
Deferred tax assets, net	5,002	4,650
Deferred tax liabilities, Depreciation	1,015	933
Deferred tax liabilities, Employee benefits	46	51
Deferred tax liabilities, Loss provisions	17	9
Deferred tax liabilities, Deferred income/expense	203	181
Deferred tax liabilities, Tax loss carryforwards
Deferred tax liabilities, Tax credit carryforwards
Deferred tax liabilities, Derivatives and hedging activities	16	43
Deferred tax liabilities, Other	297	288
Deferred tax liabilities, Gross	1,594	1,505
Deferred tax liabilities, Valuation allowance
Deferred tax liabilities, Net	$ 1,594	$ 1,505