Financing Receivable, Excluding Accrued Interest, Modified, Write-Off

No definition available.

Name:	ntrs_FinancingReceivableExcludingAccruedInterestModifiedWriteOff
Namespace Prefix:	ntrs_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- 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
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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:	dtr-types1: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
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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:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	duration

- 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:	dtr-types1: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

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 310
-SubTopic 20
-Name Accounting Standards Codification
-Section 40
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481628/310-20-40-7

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481990/310-10-45-2

+ Details

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

- Definition

Amortized cost excluding accrued interest, before allowance for credit loss, of financing receivable. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479344/326-20-45-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-3B

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-5

+ Details

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

- Definition

Amortized cost excluding accrued interest, of financing receivable 12 months after modification for debtor experiencing financial difficulty.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Subparagraph (a)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-42

+ Details

Name:	us-gaap_FinancingReceivableExcludingAccruedInterestModifiedPast12Months
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of interest income on financing receivable on nonaccrual status.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 16
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-16

+ Details

Name:	us-gaap_FinancingReceivableNonaccrualInterestIncome
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount, after valuation allowance, of financing receivable held for sale and not part of disposal group. Excludes loan covered under loss sharing agreement and loan classified as investment in debt security.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481990/310-10-45-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 948
-SubTopic 310
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477011/948-310-45-1

+ Details

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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://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 35
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-35

+ Details

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

- Details

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

- Details

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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:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
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Period Type:

Loans (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
Loans (Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 41,950.3		$ 41,950.3		$ 47,617.0
Other U.S. loans and non-U.S. loans, short duration advances	4,500.0		4,500.0		8,400.0
Demand deposits	19.0		19.0		12.1
Financing receivable, nonaccrual, interest income	0.5	$ 0.9	1.7	$ 2.3
Loans in process of foreclosure	5.2		5.2		3.5
Modified loans, charged off	0.0		8.5
Mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, held-for-sale, not part of disposal group, after valuation allowance	0.0		0.0		0.0
90 days or greater past due \| Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified	1.0		1.0
Personal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 21,116.5		$ 21,116.5		22,204.2
Personal \| Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Collateral required on Residential real estate loan, lower limit	65.00%		65.00%
Collateral required on Residential real estate loan, upper limit	80.00%		80.00%
Loans and leases	$ 6,141.2		$ 6,141.2		6,327.1
Personal \| Home Equity Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Draw period for credit line products			10 years
Loans and leases	221.1		$ 221.1		$ 228.7
Percentage of total equity credit lines			98.00%		96.00%
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 20,833.8		$ 20,833.8		$ 25,412.8