Summary of Significant Commitments (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Long-term Purchase Commitment
Commitments	$ 4,191
Commitments to Extend Credit
Long-term Purchase Commitment
Commitments	53,832	53,403
Financial Standby Letter of Credit
Long-term Purchase Commitment
Commitments	4,191	4,281
Forward Contracts
Long-term Purchase Commitment
Commitments	7,752	5,322
Noncancelable Lease Obligations
Long-term Purchase Commitment
Commitments	768	769
Private Equity Funds
Long-term Purchase Commitment
Commitments	114	121
Purchase Commitment
Long-term Purchase Commitment
Commitments	82	87
Capital Additions
Long-term Purchase Commitment
Commitments	31	29
Capital Lease Obligations
Long-term Purchase Commitment
Commitments	$ 22	$ 24

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents commitments outstanding as of the balance sheet date which obligate or represent potential claims against the assets of the Company relating to, for example, the extension of credit. Further, commitments generally represent off balance sheet arrangements that obligate the entity to deliver assets or services or enter into another obligation in the future.

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