Fair Value Measurements - Carrying Value and Estimated Fair Value of Financial Instruments (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value Of Other Financial Instrument [Line Items]
Derivatives	$ 4,423	$ 5,004
Loans and Leases Receivable, Net Amount	71,882	72,858	$ 82,005
Derivatives	3,196	4,535
Level 1 [Member]
Fair Value Of Other Financial Instrument [Line Items]
Short-term financial assets	1,115	1,235
Federal Funds Sold and Securities Purchased under Agreements to Resell	0	0
Federal funds sold and securities purchased under agreements to resell designated under fair value option	0	0
Non-derivative trading assets	7,558	3,560
Derivatives	6	12
Securities	19,906	25,145
Short-term financial liabilities	0	0
Deposits designated under fair value option	0	0
Deposits held for sale	0
Non-derivative trading liabilities	1,722	1,060
Derivatives	12	8
Short-term borrowings designated under fair value option	0	0
Long-term debt	0	0
Long-term debt designated under fair value option	0	0
Level 1 [Member] \| Commercial Loans [Member]
Fair Value Of Other Financial Instrument [Line Items]
Commercial loans designated under fair value option and held for sale	0	0
Loans held for sale	0	0
Level 1 [Member] \| Consumer Loans [Member] \| Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans held for sale	0	0
Level 1 [Member] \| Consumer Loans [Member] \| Other consumer [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans held for sale	0	0
Level 1 [Member] \| Deposits Without Fixed Maturities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Deposits	0	0
Level 1 [Member] \| Deposits With Fixed Maturities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Deposits	0	0
Level 2 [Member]
Fair Value Of Other Financial Instrument [Line Items]
Short-term financial assets	11,157	20,238
Federal Funds Sold and Securities Purchased under Agreements to Resell	32,538	29,253
Federal funds sold and securities purchased under agreements to resell designated under fair value option	80	770
Non-derivative trading assets	2,935	5,811
Derivatives	4,388	4,961
Securities	24,585	24,498
Short-term financial liabilities	2,635	2,462
Deposits designated under fair value option	6,796	6,119
Deposits held for sale	673
Non-derivative trading liabilities	524	62
Derivatives	3,173	4,511
Short-term borrowings designated under fair value option	2,032	2,672
Long-term debt	22,717	28,093
Long-term debt designated under fair value option	12,245	9,885
Level 2 [Member] \| Commercial Loans [Member]
Fair Value Of Other Financial Instrument [Line Items]
Commercial loans designated under fair value option and held for sale	471	725
Loans held for sale	177	119
Level 2 [Member] \| Consumer Loans [Member] \| Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans held for sale	5	9
Level 2 [Member] \| Consumer Loans [Member] \| Other consumer [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans held for sale	0	0
Level 2 [Member] \| Deposits Without Fixed Maturities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Deposits	100,502	112,009
Level 2 [Member] \| Deposits With Fixed Maturities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Deposits	9,782	9,749
Level 3 [Member]
Fair Value Of Other Financial Instrument [Line Items]
Short-term financial assets	32	27
Federal Funds Sold and Securities Purchased under Agreements to Resell	0	0
Federal funds sold and securities purchased under agreements to resell designated under fair value option	0	0
Non-derivative trading assets	1,932	3,068
Derivatives	29	31
Securities	111	105
Short-term financial liabilities	32	27
Deposits designated under fair value option	897	1,407
Deposits held for sale	0
Non-derivative trading liabilities	0	0
Derivatives	11	16
Short-term borrowings designated under fair value option	0	0
Long-term debt	0	0
Long-term debt designated under fair value option	641	499
Level 3 [Member] \| Commercial Loans [Member]
Fair Value Of Other Financial Instrument [Line Items]
Commercial loans designated under fair value option and held for sale	0	0
Loans held for sale	0	0
Level 3 [Member] \| Consumer Loans [Member] \| Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans held for sale	1	903
Level 3 [Member] \| Consumer Loans [Member] \| Other consumer [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans held for sale	61	71
Level 3 [Member] \| Deposits Without Fixed Maturities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Deposits	0	0
Level 3 [Member] \| Deposits With Fixed Maturities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Deposits	0	0
Carrying Value [Member]
Fair Value Of Other Financial Instrument [Line Items]
Short-term financial assets	12,304	21,500
Federal Funds Sold and Securities Purchased under Agreements to Resell	32,538	29,253
Federal funds sold and securities purchased under agreements to resell designated under fair value option	80	770
Non-derivative trading assets	12,425	12,439
Derivatives	4,423	5,004
Securities	44,677	49,719
Short-term financial liabilities	2,650	2,456
Deposits designated under fair value option	7,693	7,526
Deposits held for sale	673
Non-derivative trading liabilities	2,246	1,122
Derivatives	3,196	4,535
Short-term borrowings designated under fair value option	2,032	2,672
Long-term debt	22,080	27,355
Long-term debt designated under fair value option	12,886	10,384
Carrying Value [Member] \| Commercial Loans [Member]
Fair Value Of Other Financial Instrument [Line Items]
Commercial loans designated under fair value option and held for sale	471	725
Loans held for sale	177	119
Carrying Value [Member] \| Consumer Loans [Member] \| Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans held for sale	6	894
Carrying Value [Member] \| Consumer Loans [Member] \| Other consumer [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans held for sale	61	71
Carrying Value [Member] \| Deposits Without Fixed Maturities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Deposits	100,502	112,009
Carrying Value [Member] \| Deposits With Fixed Maturities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Deposits	9,834	9,713
Estimate of fair value [Member]
Fair Value Of Other Financial Instrument [Line Items]
Short-term financial assets	12,304	21,500
Federal Funds Sold and Securities Purchased under Agreements to Resell	32,538	29,253
Federal funds sold and securities purchased under agreements to resell designated under fair value option	80	770
Non-derivative trading assets	12,425	12,439
Derivatives	4,423	5,004
Securities	44,602	49,748
Short-term financial liabilities	2,667	2,489
Deposits designated under fair value option	7,693	7,526
Deposits held for sale	673
Non-derivative trading liabilities	2,246	1,122
Derivatives	3,196	4,535
Short-term borrowings designated under fair value option	2,032	2,672
Long-term debt	22,717	28,093
Long-term debt designated under fair value option	12,886	10,384
Estimate of fair value [Member] \| Commercial Loans [Member]
Fair Value Of Other Financial Instrument [Line Items]
Commercial loans designated under fair value option and held for sale	471	725
Loans held for sale	177	119
Estimate of fair value [Member] \| Consumer Loans [Member] \| Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans held for sale	6	912
Estimate of fair value [Member] \| Consumer Loans [Member] \| Other consumer [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans held for sale	61	71
Estimate of fair value [Member] \| Deposits Without Fixed Maturities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Deposits	100,502	112,009
Estimate of fair value [Member] \| Deposits With Fixed Maturities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Deposits	9,782	9,749
Commercial Portfolio Segment [Member] \| Level 1 [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans and Leases Receivable, Net Amount	0	0
Commercial Portfolio Segment [Member] \| Level 2 [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans and Leases Receivable, Net Amount	0	0
Commercial Portfolio Segment [Member] \| Level 3 [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans and Leases Receivable, Net Amount	54,210	54,938
Commercial Portfolio Segment [Member] \| Carrying Value [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans and Leases Receivable, Net Amount	52,427	53,286
Commercial Portfolio Segment [Member] \| Estimate of fair value [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans and Leases Receivable, Net Amount	54,210	54,938
Other consumer [Member] \| Level 1 [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans and Leases Receivable, Net Amount	0	0
Other consumer [Member] \| Level 2 [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans and Leases Receivable, Net Amount	0	0
Other consumer [Member] \| Level 3 [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans and Leases Receivable, Net Amount	18,598	18,833
Other consumer [Member] \| Carrying Value [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans and Leases Receivable, Net Amount	19,455	19,572
Other consumer [Member] \| Estimate of fair value [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans and Leases Receivable, Net Amount	$ 18,598	$ 18,833

Deposits Held for Sale, Fair Value

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- Definition

Fair Value of Commercial Syndicated Loans Held For Sale

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No definition available.

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- Definition

Interest bearing deposits domestic fair value option disclosure.

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No definition available.

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- Definition

This element represents the portion of long term debt that the entity has elected to value at fair value under the fair value option.

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No definition available.

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- Definition

Non-derivative trading assets fair value disclosure.

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Non derivative trading liability.

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Securities, Fair Value Disclosure

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- Definition

Securities Purchased under Agreements to Resell, Fair Value Option

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No definition available.

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- Definition

Short-term financial assets fair value disclosure.

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No definition available.

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- Definition

Short-term Financial Liabilities, Fair Value

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No definition available.

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- Definition

Fair value portion of deposit liabilities held by the entity, including, but not limited to, foreign and domestic, interest and noninterest bearing, demand deposits, saving deposits, negotiable orders of withdrawal (NOW) and time deposits.

+ References

No definition available.

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- Definition

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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- Definition

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Fair value portion of federal funds sold and securities borrowed or purchased under agreements to resell.

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- Definition

Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements and loans held for sale.

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- Definition

Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.

+ References

No definition available.

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- Definition

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.

+ References

No definition available.

+ Details

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- 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 the amount of short-term debt existing as of the balance sheet date.

+ References

No definition available.

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