Summary of Significant Commitments (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011
Commitments to Extend Credit
Long-term Purchase Commitment [Line Items]
Commitments	$ 52,274	$ 47,719	$ 46,019
Financial Standby Letter of Credit
Long-term Purchase Commitment [Line Items]
Commitments	4,558	4,744	4,949
Forward Contracts
Long-term Purchase Commitment [Line Items]
Commitments	8,749	5,705	4,602
Noncancelable Lease Obligations [Member]
Long-term Purchase Commitment [Line Items]
Commitments	782	851	856
Private Equity Funds
Long-term Purchase Commitment [Line Items]
Commitments	137	166	178
Purchase Commitment
Long-term Purchase Commitment [Line Items]
Commitments	97	115	117
Capital Additions
Long-term Purchase Commitment [Line Items]
Commitments	45	41	42
Capital Lease Obligations
Long-term Purchase Commitment [Line Items]
Commitments	$ 16	$ 26	$ 25

- 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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