Derivative Instruments - Derivative Positions of Company (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Derivative Financial Instruments, Assets [Member]
Derivatives, Fair Value [Line Items]
Total fair value of derivative positions	$ 1,806	$ 1,913
Netting	(418)	(294)
Total	1,388	1,619
Derivative Financial Instruments, Liabilities [Member]
Derivatives, Fair Value [Line Items]
Total fair value of derivative positions	2,183	2,554
Netting	(1,549)	(1,889)
Total	$ 634	$ 665

Fair values as of the balance sheet date of all assets resulting from contracts that meet the criteria of being accounted for as derivative instruments, net of the effects of master netting arrangements.

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Fair value of derivative asset, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position.

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- Definition

Fair value of derivative liability, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position.

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- Definition

Fair values as of the balance sheet date of all liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments, net of the effects of master netting arrangements.

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