Fair Value Measurements - Fair Value Disclosures of Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
ASSETS
Loans, net of allowance	$ 157
Derivative assets	693	945
LIABILITIES
Derivative liabilities	584	1,026
Carrying Amount [Member]
ASSETS
Cash and short-term investments	4,525	4,213
Trading account assets	605	623
Securities available for sale	12,094	16,012
Held-to-maturity securities	3,931	2,109
Other investments	1,064	1,163
Loans, net of allowance	51,934	48,571
Loans held for sale	599	728
Mortgage servicing assets	204	173
Derivative assets	693	945
LIABILITIES
Deposits with no stated maturity	58,132	51,014
Time deposits	7,861	10,942
Short-term borrowings	1,896	2,048
Long-term debt	6,847	9,520
Derivative liabilities	584	1,026
Fair Value [Member]
ASSETS
Cash and short-term investments	4,525	4,213
Trading account assets	605	623
Securities available for sale	12,094	16,012
Held-to-maturity securities	3,992	2,133
Other investments	1,064	1,163
Loans, net of allowance	51,046	47,561
Loans held for sale	599	728
Mortgage servicing assets	238	245
Derivative assets	693	945
LIABILITIES
Deposits with no stated maturity	58,132	51,014
Time deposits	8,020	11,253
Short-term borrowings	1,896	2,048
Long-term debt	7,392	9,792
Derivative liabilities	584	1,026
Fair Value [Member] \| Level 1 [Member]
ASSETS
Cash and short-term investments	4,254
Trading account assets	2
Securities available for sale	43
Derivative assets	54
LIABILITIES
Time deposits	408
Long-term debt	2,807
Derivative liabilities	54
Fair Value [Member] \| Level 2 [Member]
ASSETS
Cash and short-term investments	271
Trading account assets	600
Securities available for sale	12,051
Held-to-maturity securities	3,992
Other investments	396
Derivative assets	1,883
LIABILITIES
Deposits with no stated maturity	58,132
Time deposits	7,612
Short-term borrowings	1,896
Long-term debt	4,585
Derivative liabilities	1,331
Fair Value [Member] \| Level 3 [Member]
ASSETS
Trading account assets	3
Other investments	668
Loans, net of allowance	51,046
Loans held for sale	599
Mortgage servicing assets	238
Derivative assets	26
LIABILITIES
Derivative liabilities	2
Fair Value [Member] \| Netting Adjustment [Member]
ASSETS
Derivative assets	(1,270)
LIABILITIES
Derivative liabilities	$ (803)

Cash and short term investments fair value.

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Mortgage servicing assets fair value.

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Other short term investments fair value.

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Short term borrowing fair value.

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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 Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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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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The fair value amount of long-term debt 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.

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