Financing Receivable, Nonaccrual Troubled Debt Restructuring

No definition available.

Name:	ntrs_FinancingReceivableNonaccrualTroubledDebtRestructuring
Namespace Prefix:	ntrs_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line of credit draw down period for equity credit line products.

+ References

No definition available.

+ Details

Name:	ntrs_LineOfCreditDrawDownPeriod
Namespace Prefix:	ntrs_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents short duration advances, primarily related to overdrafts associated with the timing of custody client's investments included in other U.S. and non-U.S. loans.

+ References

No definition available.

+ Details

Name:	ntrs_LoansReceivableOverdraftAdvances
Namespace Prefix:	ntrs_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Lower Limit of Generally Required Loan to Collateral Value for Residential Real Estate Loans

+ References

No definition available.

+ Details

Name:	ntrs_LowerLimitOfGenerallyRequiredLoanToCollateralValueForResidentialRealEstateLoans
Namespace Prefix:	ntrs_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of overdrawn money in accounts that may bear interest and that the depositor is entitled to withdraw at any time without prior notice, which have been reclassified to loans.

+ References

No definition available.

+ Details

Name:	ntrs_OverdrawnDemandDepositAccounts
Namespace Prefix:	ntrs_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Percentage of Total Equity Credit Lines

+ References

No definition available.

+ Details

Name:	ntrs_PercentageofTotalEquityCreditLines
Namespace Prefix:	ntrs_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Upper Limit of Generally Required Loan to Collateral Value for Residential Real Estate loans

+ References

No definition available.

+ Details

Name:	ntrs_UpperLimitOfGenerallyRequiredLoanToCollateralValueForResidentialRealEstateLoans
Namespace Prefix:	ntrs_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- 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.

+ Details

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

- Definition

Amount of financing receivable modified as troubled debt restructuring.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953676-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=118939409&loc=d3e18845-111554

+ Details

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

- Definition

Number of financing receivable contracts modified as troubled debt restructuring within previous 12 months, with subsequent payment default.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953682-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of unfunded portion of contractual agreement to lend funds to borrower for financing receivable modified as troubled debt restructuring.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118939409&loc=d3e18794-111554

+ Details

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

- Definition

Amount, after allowance for bad debt, of loan receivables held-for-sale that are not part of a disposal group. Excludes loans and leases covered under loss sharing agreements and loans classified as debt securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=118952595&loc=d3e4428-111522

+ Details

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

- Definition

Recorded investment of consumer mortgage loan receivables secured by residential real estate properties for which formal foreclosure proceedings are in process.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 35
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL49126937-111524

+ Details

Name:	us-gaap_MortgageLoansInProcessOfForeclosureAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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 326
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919230-210447

+ Details

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

- Definition

Carrying amount as of the balance sheet date of other real estate and foreclosed assets. Other real estate may include real estate investments, real estate loans that qualify as investments in real estate, and premises that are no longer used in operations may also be included in real estate owned. Foreclosed assets include all assets obtained in full or partial satisfaction of a debt arrangement through foreclosure proceedings.

+ 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 210.9-03.10(4))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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

- Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_HomeEquityLoanMember
Namespace Prefix:
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Period Type:

Loans and Leases (Narrative) (Details)	3 Months Ended	13 Months Ended
Loans and Leases (Narrative) (Details)	Mar. 31, 2020 USD ($)	Jun. 30, 2019 Loan	Jun. 30, 2018 Loan	Dec. 31, 2019 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases	$ 37,837,700,000			$ 31,409,600,000
Other U.S. loans and non-U.S. loans, short duration advances	3,800,000,000			1,100,000,000
Demand deposits	26,700,000			90,400,000
Financing receivable, nonaccrual troubled debt restructuring	73,400,000			54,900,000
Financing receivable, recorded investment	22,600,000			27,700,000
Financing receivable, troubled debt restructuring, commitment to lend	11,700,000			8,200,000
Foreclosed real estate properties, carrying value	1,600,000			3,200,000
Loans in process of foreclosure	20,800,000
Lease Agreements
Accounts, Notes, Loans and Financing Receivable [Line Items]
Held for sale	52,800,000			53,600,000
Mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Held for sale				0
Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, troubled debt restructuring, subsequent default, number of contracts \| Loan		0	0
Personal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases	$ 18,100,900,000			17,408,300,000
Personal \| Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Collateral required on residential real estate loan, lower limit	65.00%
Collateral required on residential real estate loan, upper limit	80.00%
Loans and Leases	$ 6,074,300,000			6,095,000,000.0
Personal \| Home Equity Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Draw period for credit line products	10 years
Loans and Leases	$ 429,600,000			$ 448,500,000
Percentage of total equity credit lines	96.00%			97.00%