Commitments to originate real estate loans for sale.

No definition available.

Name:	mtb_CommitmentsToOriginateRealEstateLoansForSale
Namespace Prefix:	mtb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Commitments to sell real estate loans net.

+ References

No definition available.

+ Details

Name:	mtb_CommitmentsToSellRealEstateLoansNet
Namespace Prefix:	mtb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Interest rate swap agreements used for interest rate risk management.

+ References

No definition available.

+ Details

Name:	mtb_InterestRateSwapAgreementsUsedForInterestRateRiskManagement
Namespace Prefix:	mtb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount before allowance of consumer installment revolving and home equity loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts.

+ References

No definition available.

+ Details

Name:	mtb_LoansAndLeasesReceivableConsumerInstallmentRevolvingAndHomeEquity
Namespace Prefix:	mtb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Other credit-related commitments.

+ References

No definition available.

+ Details

Name:	mtb_OtherCreditRelatedCommitments
Namespace Prefix:	mtb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Other financial instruments.

+ References

No definition available.

+ Details

Name:	mtb_OtherFinancialInstrumentsAbstract
Namespace Prefix:	mtb_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of domestic interest-bearing checking and savings accounts, which may include money market accounts, NOW accounts, interest-bearing corporate checking accounts, brokered deposits and other savings accounts.

+ References

No definition available.

+ Details

Name:	mtb_SavingsAndInterestCheckingDeposits
Namespace Prefix:	mtb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Interest, dividends, rents, ancillary and other revenues earned but not yet received by the entity on its investments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(4))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(3))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(10))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

+ Details

Name:	us-gaap_AccruedInvestmentIncomeReceivable
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3044-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=124098289&loc=d3e6676-107765

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.1)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_CashAndCashEquivalentsAtCarryingValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The aggregate of all foreign interest-bearing and noninterest-bearing deposit liabilities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 235
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-05(a))
-URI http://asc.fasb.org/extlink&oid=120399901&loc=d3e537907-122884

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.12(a))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

+ Details

Name:	us-gaap_DepositsForeign
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount after offset of short term borrowing where a bank borrows, at the federal funds rate, from another bank and securities that an entity sells and agrees to repurchase at a specified date for a specified price.

+ References

+ Details

Name:	us-gaap_FederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchase
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

Name:	us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

Name:	us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

For banks and other depository institutions (including Federal Reserve Banks, if applicable): Interest-bearing deposits in other financial institutions for relatively short periods of time including, for example, certificates of deposits, which are presented separately from cash on the balance sheet.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=117340910&loc=d3e59706-112781

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.2)
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

+ Details

Name:	us-gaap_InterestBearingDepositsInBanks
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of interest payable on debt, including, but not limited to, trade payables.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.15(5))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.15(a))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

+ Details

Name:	us-gaap_InterestPayableCurrentAndNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Sum of the carrying amounts as of the balance sheet date of all investments.

+ References

+ Details

Name:	us-gaap_Investments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SAB Topic 6.L.1)
-URI http://asc.fasb.org/extlink&oid=122038336&loc=d3e74567-122707

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953423-111524

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (b)(1)(ii)
-URI http://asc.fasb.org/extlink&oid=121614798&loc=d3e15032-111544

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953423-111524

+ Details

Name:	us-gaap_LoansAndLeasesReceivableAllowance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

Name:	us-gaap_LoansAndLeasesReceivableGrossCarryingAmountAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- 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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=124259787&loc=d3e4428-111522

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7)
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

+ Details

Name:	us-gaap_LoansAndLeasesReceivableNetReportedAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=123466204&loc=SL6031897-161870

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 55
-Paragraph 69C
-URI http://asc.fasb.org/extlink&oid=123466577&loc=SL123495737-112612

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 4: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 55
-Paragraph 69B
-URI http://asc.fasb.org/extlink&oid=123466577&loc=SL123495735-112612

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1D
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495340-112611

Reference 7: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_LongTermDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of domestic noninterest-bearing deposits held by the entity, which may include demand deposits, checking, brokered and retail deposits.

+ References

+ Details

Name:	us-gaap_NoninterestBearingDepositLiabilitiesDomestic
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount, before allowance for credit loss, of financing receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7A
-URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953401-111524

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 55
-Paragraph 79
-URI http://asc.fasb.org/extlink&oid=124267575&loc=SL82922352-210448

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919253-210447

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919230-210447

Reference 6: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 55
-Paragraph 80
-URI http://asc.fasb.org/extlink&oid=124267575&loc=SL82922355-210448

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph (a)
-Subparagraph (1)

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph (a)
-Subparagraph (2)

Reference 9: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher SEC
-Name Regulation S-K (SK)
-Number 229
-Section 1404
-Paragraph (a)

+ Details

Name:	us-gaap_NotesReceivableGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of time deposit liabilities, including certificates of deposit.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 405
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=116652737&loc=d3e64164-112818

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.12)
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

+ Details

Name:	us-gaap_TimeDeposits
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value portion of liabilities pertaining to principal and customer trading transactions, or which may be incurred with the objective of generating a profit from short-term fluctuations in price as part of an entity's market-making, hedging and proprietary trading. Examples include, but are not limited to, short positions in securities, derivatives and commodities.

+ References

No definition available.

+ Details

Name:	us-gaap_TradingLiabilitiesFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

+ Details

Name:	us-gaap_TradingSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=mtb_CommercialLoansAndLeasesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=mtb_CommercialRealEstateExcludingResidentialBuilderAndDeveloperAndOtherConstructionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=mtb_ResidentialRealEstateLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementBasisAxis=us-gaap_CarryingReportedAmountFairValueDisclosureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementBasisAxis=us-gaap_EstimateOfFairValueFairValueDisclosureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Fair Value Measurements - Carrying Amounts and Estimated Fair Value for Financial Instrument Assets (Liabilities) (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Financial assets:
Interest-bearing deposits at banks	$ 38,445,788		$ 23,663,810
Investment securities	6,447,622		7,045,697
Loans and leases:
Allowance for credit losses	(1,515,024)	$ (1,575,128)	(1,736,387)	$ (1,758,505)	$ (1,638,236)	$ (1,051,071)
Loans and leases, net	92,067,870		96,799,480
Financial liabilities:
Noninterest-bearing deposits	(56,542,309)		(47,572,884)
Savings and interest-checking deposits	(69,195,960)		(67,680,840)
Time deposits	(2,963,027)		(3,899,910)
Deposits at Cayman Islands office			(652,104)
Long-term borrowings	(3,500,391)		(4,382,193)
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Financial assets:
Cash and cash equivalents	1,351,944		1,497,457
Trading account assets	50,335		50,060
Investment securities	75,169		63,129
Significant Observable Inputs (Level 2) [Member]
Financial assets:
Cash and cash equivalents	127,768		55,286
Interest-bearing deposits at banks	38,445,788		23,663,810
Trading account assets	574,221		1,018,521
Investment securities	6,364,735		7,005,571
Loans and leases:
Loans and leases, net	4,461,715		4,413,566
Accrued interest receivable	378,433		419,936
Financial liabilities:
Noninterest-bearing deposits	(56,542,309)		(47,572,884)
Savings and interest-checking deposits	(69,195,960)		(67,680,840)
Time deposits	(2,967,906)		(3,919,367)
Deposits at Cayman Islands office			(652,104)
Short-term borrowings	(103,548)		(59,482)
Long-term borrowings	(3,605,637)		(4,490,433)
Accrued interest payable	(38,808)		(59,916)
Trading account liabilities	(92,649)		(116,902)
Other financial instruments:
Commitments to sell real estate loans	9,734		(18,429)
Interest rate swap agreements used for interest rate risk management	1,384		1,076
Significant Unobservable Inputs (Level 3) [Member]
Financial assets:
Investment securities	61,929		70,289
Loans and leases:
Consumer loans	17,935,068		16,554,050
Loans and leases, net	88,498,523		93,266,904
Other financial instruments:
Commitments to originate real estate loans for sale	20,145		43,234
Other credit-related commitments	(124,145)		(133,354)
Commercial Loans And Leases [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Loans and leases:
Commercial loans and leases	22,315,530		27,220,699
Commercial [Member] \| Significant Observable Inputs (Level 2) [Member]
Loans and leases:
Commercial loans and leases	558,970		277,911
Commercial [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Loans and leases:
Commercial loans and leases	35,753,119		36,538,669
Residential Real Estate Loans [Member] \| Significant Observable Inputs (Level 2) [Member]
Loans and leases:
Commercial loans and leases	3,902,745		4,135,655
Residential Real Estate Loans [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Loans and leases:
Commercial loans and leases	12,494,806		12,953,486
Carrying Amount [Member]
Financial assets:
Cash and cash equivalents	1,479,712		1,552,743
Interest-bearing deposits at banks	38,445,788		23,663,810
Trading account assets	624,556		1,068,581
Investment securities	6,447,622		7,045,697
Loans and leases:
Consumer loans	17,834,648		16,570,421
Allowance for credit losses	(1,515,024)		(1,736,387)
Loans and leases, net	92,067,870		96,799,480
Accrued interest receivable	378,433		419,936
Financial liabilities:
Noninterest-bearing deposits	(56,542,309)		(47,572,884)
Savings and interest-checking deposits	(69,195,960)		(67,680,840)
Time deposits	(2,963,027)		(3,899,910)
Deposits at Cayman Islands office			(652,104)
Short-term borrowings	(103,548)		(59,482)
Long-term borrowings	(3,500,391)		(4,382,193)
Accrued interest payable	(38,808)		(59,916)
Trading account liabilities	(92,649)		(116,902)
Other financial instruments:
Commitments to originate real estate loans for sale	20,145		43,234
Commitments to sell real estate loans	9,734		(18,429)
Other credit-related commitments	(124,145)		(133,354)
Interest rate swap agreements used for interest rate risk management	1,384		1,076
Carrying Amount [Member] \| Commercial Loans And Leases [Member]
Loans and leases:
Commercial loans and leases	22,514,940		27,574,564
Carrying Amount [Member] \| Commercial [Member]
Loans and leases:
Commercial loans and leases	37,023,952		37,637,889
Carrying Amount [Member] \| Residential Real Estate Loans [Member]
Loans and leases:
Commercial loans and leases	16,209,354		16,752,993
Cumulative Amount of Fair Value Hedging Adjustment Increasing (Decreasing) the Carrying Amount [Member]
Financial assets:
Cash and cash equivalents	1,479,712		1,552,743
Interest-bearing deposits at banks	38,445,788		23,663,810
Trading account assets	624,556		1,068,581
Investment securities	6,501,833		7,138,989
Loans and leases:
Consumer loans	17,935,068		16,554,050
Loans and leases, net	92,960,238		97,680,470
Accrued interest receivable	378,433		419,936
Financial liabilities:
Noninterest-bearing deposits	(56,542,309)		(47,572,884)
Savings and interest-checking deposits	(69,195,960)		(67,680,840)
Time deposits	(2,967,906)		(3,919,367)
Deposits at Cayman Islands office			(652,104)
Short-term borrowings	(103,548)		(59,482)
Long-term borrowings	(3,605,637)		(4,490,433)
Accrued interest payable	(38,808)		(59,916)
Trading account liabilities	(92,649)		(116,902)
Other financial instruments:
Commitments to originate real estate loans for sale	20,145		43,234
Commitments to sell real estate loans	9,734		(18,429)
Other credit-related commitments	(124,145)		(133,354)
Interest rate swap agreements used for interest rate risk management	1,384		1,076
Cumulative Amount of Fair Value Hedging Adjustment Increasing (Decreasing) the Carrying Amount [Member] \| Commercial Loans And Leases [Member]
Loans and leases:
Commercial loans and leases	22,315,530		27,220,699
Cumulative Amount of Fair Value Hedging Adjustment Increasing (Decreasing) the Carrying Amount [Member] \| Commercial [Member]
Loans and leases:
Commercial loans and leases	36,312,089		36,816,580
Cumulative Amount of Fair Value Hedging Adjustment Increasing (Decreasing) the Carrying Amount [Member] \| Residential Real Estate Loans [Member]
Loans and leases:
Commercial loans and leases	$ 16,397,551		$ 17,089,141