Fair Value Measurements - Fair Value Disclosures of Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013
ASSETS
Other investments	$ 899	$ 969	$ 1,059
Loans, net of allowance	143	147	154
Loans held for sale			12
Derivative assets	427	407	609
LIABILITIES
Short-term borrowings	464	343	378
Derivative liabilities	408	414	524
Level 1 [Member]
ASSETS
Loans held for sale
Level 2 [Member]
ASSETS
Loans held for sale
Level 3 [Member]
ASSETS
Loans held for sale			12
Carrying Amount [Member]
ASSETS
Cash and short-term investments	3,331	6,207	3,702
Trading account assets	840	738	701
Securities available for sale	12,359	12,346	13,496
Held-to-maturity securities	4,826	4,756	3,721
Other investments	899	969	1,059
Loans, net of allowance	54,611	53,609	51,681
Loans held for sale	401	611	434
Mortgage servicing assets	320	332	201
Derivative assets	427	407	609
LIABILITIES
Deposits with no stated maturity	60,130	62,425	56,810
Time deposits	7,136	6,837	7,844
Short-term borrowings	1,181	1,877	2,328
Long-term debt	7,712	7,650	7,785
Derivative liabilities	408	414	524
Fair Value [Member]
ASSETS
Cash and short-term investments	3,331	6,207	3,702
Trading account assets	840	738	701
Securities available for sale	12,359	12,346	13,496
Held-to-maturity securities	4,733	4,617	3,779
Other investments	899	969	1,059
Loans, net of allowance	53,211	52,102	50,926
Loans held for sale	401	611	434
Mortgage servicing assets	373	386	244
Derivative assets	427	407	609
LIABILITIES
Deposits with no stated maturity	60,130	62,425	56,810
Time deposits	7,216	6,926	7,982
Short-term borrowings	1,181	1,877	2,328
Long-term debt	8,069	8,008	8,263
Derivative liabilities	408	414	524
Fair Value [Member] \| Level 1 [Member]
ASSETS
Cash and short-term investments	3,331	6,207	3,702
Trading account assets	4	4	5
Securities available for sale	21	20	43
Held-to-maturity securities
Other investments
Loans, net of allowance
Loans held for sale
Mortgage servicing assets
Derivative assets	51	56	57
LIABILITIES
Deposits with no stated maturity
Time deposits	617	558	522
Short-term borrowings	3	2	3
Long-term debt	7,610	7,611	2,781
Derivative liabilities	43	49	54
Fair Value [Member] \| Level 2 [Member]
ASSETS
Cash and short-term investments
Trading account assets	836	734	693
Securities available for sale	12,338	12,326	13,453
Held-to-maturity securities	4,733	4,617	3,779
Other investments	335	392	394
Loans, net of allowance
Loans held for sale
Mortgage servicing assets
Derivative assets	1,063	1,134	1,630
LIABILITIES
Deposits with no stated maturity	60,130	62,425	56,810
Time deposits	6,599	6,368	7,460
Short-term borrowings	1,178	1,875	2,325
Long-term debt	459	397	5,482
Derivative liabilities	812	864	1,164
Fair Value [Member] \| Level 3 [Member]
ASSETS
Cash and short-term investments
Trading account assets			3
Securities available for sale
Held-to-maturity securities
Other investments	564	577	665
Loans, net of allowance	53,211	52,102	50,926
Loans held for sale	401	611	434
Mortgage servicing assets	373	386	244
Derivative assets	26	29	37
LIABILITIES
Deposits with no stated maturity
Time deposits
Short-term borrowings
Long-term debt
Derivative liabilities	1	1	2
Fair Value [Member] \| Netting Adjustment [Member]
ASSETS
Cash and short-term investments
Trading account assets
Securities available for sale
Held-to-maturity securities
Other investments
Loans, net of allowance
Loans held for sale
Mortgage servicing assets
Derivative assets	(713)	(812)	(1,115)
LIABILITIES
Deposits with no stated maturity
Time deposits
Short-term borrowings
Long-term debt
Derivative liabilities	$ (448)	$ (500)	$ (696)

Deposits with no stated maturity 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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Cash includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the customer may deposit additional funds at any time and effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid Investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months. Short-term investments, exclusive of cash equivalents, generally consist of marketable securities intended to be sold within one year (or the normal operating cycle if longer) and may include trading securities, available-for-sale securities, or held-to-maturity securities (if maturing within one year), as applicable.

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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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Other investments not otherwise specified in the taxonomy that will be realized in a short period of time, usually less than one year or the normal operating cycle, whichever is longer.

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