Derivative Instruments and Other Financial Instruments Used For Hedging - Summary of Offsetting Assets and Liabilities (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Assets/Liabilities, Financial Assets	$ 1,144	$ 1,443
Gross Amounts of Recognized Assets/Liabilities, Financial Liabilities	1,011	1,320
Financial Liabilities [Member]
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Assets/Liabilities, Financial Liabilities	1,015	1,325
Gross Amounts Offset in Balance Sheet, Financial Liabilities	448	449
Net Amounts Presented in Balance Sheet, Financial Liabilities	567	876
Net Amount, Financial Liabilities	312	259
Financial Liabilities [Member] \| Securities purchased under resale agreements [Member]
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Assets/Liabilities, Financial Liabilities	4	5
Net Amounts Presented in Balance Sheet, Financial Liabilities	4	5
Financial Liabilities [Member] \| Derivative Liabilities [Member]
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Assets/Liabilities, Financial Liabilities	1,011	1,320
Gross Amounts Offset in Balance Sheet, Financial Liabilities	448	449
Net Amounts Presented in Balance Sheet, Financial Liabilities	563	871
Net Amount, Financial Liabilities	312	259
Financial Assets [Member]
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Assets/Liabilities, Financial Assets	1,159	1,462
Gross Amounts Offset in Balance Sheet, Financial Assets	444	370
Net Amounts Presented in Balance Sheet, Financial Assets	715	1,092
Net Amount, Financial Assets	638	1,050
Financial Assets [Member] \| Derivative Assets [Member]
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Assets/Liabilities, Financial Assets	1,144	1,443
Gross Amounts Offset in Balance Sheet, Financial Assets	444	370
Net Amounts Presented in Balance Sheet, Financial Assets	700	1,073
Net Amount, Financial Assets	638	1,050
Financial Assets [Member] \| Securities purchased under resale agreements [Member]
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Assets/Liabilities, Financial Assets	15	19
Net Amounts Presented in Balance Sheet, Financial Assets	15	19
Financial Instruments [Member] \| Financial Liabilities [Member]
Derivatives, Fair Value [Line Items]
Gross Amount Not Offset in Balance Sheet, Financial Liabilities	253	496
Financial Instruments [Member] \| Financial Liabilities [Member] \| Securities purchased under resale agreements [Member]
Derivatives, Fair Value [Line Items]
Gross Amount Not Offset in Balance Sheet, Financial Liabilities	4	5
Financial Instruments [Member] \| Financial Liabilities [Member] \| Derivative Liabilities [Member]
Derivatives, Fair Value [Line Items]
Gross Amount Not Offset in Balance Sheet, Financial Liabilities	249	491
Financial Instruments [Member] \| Financial Assets [Member]
Derivatives, Fair Value [Line Items]
Gross Amount Not Offset in Balance Sheet, Financial Assets	77	40
Financial Instruments [Member] \| Financial Assets [Member] \| Derivative Assets [Member]
Derivatives, Fair Value [Line Items]
Gross Amount Not Offset in Balance Sheet, Financial Assets	62	21
Financial Instruments [Member] \| Financial Assets [Member] \| Securities purchased under resale agreements [Member]
Derivatives, Fair Value [Line Items]
Gross Amount Not Offset in Balance Sheet, Financial Assets	15	19
Cash Collateral Received/Pledged [Member] \| Financial Liabilities [Member]
Derivatives, Fair Value [Line Items]
Gross Amount Not Offset in Balance Sheet, Financial Liabilities	2	121
Cash Collateral Received/Pledged [Member] \| Financial Liabilities [Member] \| Derivative Liabilities [Member]
Derivatives, Fair Value [Line Items]
Gross Amount Not Offset in Balance Sheet, Financial Liabilities	2	121
Cash Collateral Received/Pledged [Member] \| Financial Assets [Member]
Derivatives, Fair Value [Line Items]
Gross Amount Not Offset in Balance Sheet, Financial Assets		2
Cash Collateral Received/Pledged [Member] \| Financial Assets [Member] \| Derivative Assets [Member]
Derivatives, Fair Value [Line Items]
Gross Amount Not Offset in Balance Sheet, Financial Assets		$ 2

Fair value of the gross assets less the gross liabilities of a derivative asset or group of derivative assets.

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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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The amount as of the balance sheet date of the fair value of derivative assets that in accordance with the entity's accounting policy was not offset against an obligation to return cash collateral under a master netting arrangement.

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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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Fair value of the gross liabilities less the gross assets of a derivative liability or group of derivative liabilities.

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