Debt Instrument, Liquidation Amount Per Share

No definition available.

Name:	ntrs_DebtInstrumentLiquidationAmountPerShare
Namespace Prefix:	ntrs_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Subject to certain exceptions, the maximum consecutive periods that the Corporation can defer payment of interest provided that no extension period may extend beyond the stated maturity date.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

+ References

No definition available.

+ Details

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Balance Type:	na
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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.

+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentMaturityDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash inflow associated with security instrument that either represents a creditor or an ownership relationship with the holder of the investment security with a maturity of beyond one year or normal operating cycle, if longer. Includes proceeds from (a) debt, (b) capital lease obligations, (c) mandatory redeemable capital securities, and (d) any combination of (a), (b), or (c).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (a),(b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3255-108585

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

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- Details

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- Details

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- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Floating Rate Capital Debt - Narrative (Detail) - USD ($)	1 Months Ended		12 Months Ended
	Apr. 30, 1997	Jan. 31, 1997	Dec. 31, 2017
NTC Capital I Subordinated Debentures due January 15, 2027
Debt Instrument [Line Items]
Floating rate capital securities, issued		$ 150,000,000
Floating rate capital securities, due date	Jan. 15, 2027
Liquidation amount per Security		$ 1,000
Interest rate on the securities			Three-month LIBOR plus 0.52%
Maximum consecutive periods on the deferred payment of interest			20 Quarterly periods
NTC Capital I Subordinated Debentures due January 15, 2027 \| Group Two
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate		0.52%
NTC Capital II Subordinated Debentures due April 15, 2027
Debt Instrument [Line Items]
Floating rate capital securities, issued	$ 120,000,000
Liquidation amount per Security	$ 1,000
Interest rate on the securities			Three-month LIBOR plus 0.59%
Maximum consecutive periods on the deferred payment of interest			20 Quarterly periods
NTC Capital II Subordinated Debentures due April 15, 2027 \| Group Two
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	0.59%
London Interbank Offered Rate (LIBOR) \| NTC Capital I Subordinated Debentures due January 15, 2027
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate			0.605%
London Interbank Offered Rate (LIBOR) \| NTC Capital II Subordinated Debentures due April 15, 2027
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate			0.679%