Fair Value Measurements - Fair Value Disclosures of Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
ASSETS
Loans, net of allowance	$ 151	$ 157	$ 73
Derivative assets	461	693	818
LIABILITIES
Derivative liabilities	456	584	763
Carrying Amount [Member]
ASSETS
Cash and short-term investments	4,278	4,525	2,933
Trading account assets	592	605	679
Securities available for sale	13,253	12,094	13,205
Held-to-maturity securities	4,750	3,931	4,352
Other investments	1,037	1,064	1,186
Loans, net of allowance	52,405	51,934	48,717
Loans held for sale	402	599	656
Mortgage servicing assets	330	204	186
Derivative assets	461	693	818
LIABILITIES
Deposits with no stated maturity	60,170	58,132	52,495
Time deposits	7,551	7,861	9,672
Short-term borrowings	1,945	1,896	2,078
Long-term debt	6,666	6,847	7,521
Derivative liabilities	456	584	763
Fair Value [Member]
ASSETS
Cash and short-term investments	4,278	4,525	2,933
Trading account assets	592	605	679
Securities available for sale	13,253	12,094	13,205
Held-to-maturity securities	4,716	3,992	4,396
Other investments	1,037	1,064	1,186
Loans, net of allowance	51,019	51,046	47,912
Loans held for sale	402	599	656
Mortgage servicing assets	387	238	237
Derivative assets	461	693	818
LIABILITIES
Deposits with no stated maturity	60,170	58,132	52,495
Time deposits	7,672	8,020	9,888
Short-term borrowings	1,945	1,896	2,078
Long-term debt	7,031	7,392	7,845
Derivative liabilities	456	584	763
Fair Value [Member] \| Level 1 [Member]
ASSETS
Cash and short-term investments	3,944	4,254	2,595
Trading account assets	3	2	3
Securities available for sale	22	43	20
Other investments			11
Derivative assets	85	54	81
LIABILITIES
Time deposits	545	408	617
Short-term borrowings	4		3
Long-term debt	6,247	2,807	3,890
Derivative liabilities	78	54	81
Fair Value [Member] \| Level 2 [Member]
ASSETS
Cash and short-term investments	334	271	338
Trading account assets	589	600	618
Securities available for sale	13,231	12,051	13,185
Held-to-maturity securities	4,716	3,992	4,396
Other investments	393	396	401
Derivative assets	1,337	1,883	2,078
LIABILITIES
Deposits with no stated maturity	60,170	58,132	52,495
Time deposits	7,127	7,612	9,271
Short-term borrowings	1,941	1,896	2,075
Long-term debt	784	4,585	3,955
Derivative liabilities	1,010	1,331	1,560
Fair Value [Member] \| Level 3 [Member]
ASSETS
Trading account assets		3	58
Other investments	644	668	774
Loans, net of allowance	51,019	51,046	47,912
Loans held for sale	402	599	656
Mortgage servicing assets	387	238	237
Derivative assets	31	26	41
LIABILITIES
Derivative liabilities	1	2	2
Fair Value [Member] \| Netting Adjustment [Member]
ASSETS
Derivative assets	(992)	(1,270)	(1,382)
LIABILITIES
Derivative liabilities	$ (633)	$ (803)	$ (880)

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Mortgage servicing assets 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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