Debt Instrument, Liquidation Amount Per Share

No definition available.

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- 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

Phase Out Of Tier Capital Treatment Annual Incremental Percentage

+ References

No definition available.

+ Details

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

- Definition

Phase Out Of Tier Capital Treatment Percentage

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Tier 1 Capital Securities, Phase Out Period

+ References

No definition available.

+ Details

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Period Type:	duration

- Definition

Tier 1 Capital Securities, Phase Out Period, Start Date

+ References

No definition available.

+ Details

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Data Type:	xbrli:dateItemType
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

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
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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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Description of the interest rate as being fixed or variable, and, if variable, identification of the index or rate on which the interest rate is based and the number of points or percentage added to that index or rate to set the rate, and other pertinent information, such as frequency of rate resets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 2: 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)(1))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Balance Type:	na
Period Type:	duration

- 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 SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 2: 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

-Glossary Financing Activities

-URI http://asc.fasb.org/extlink&oid=6513228

Reference 2: 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=31042434&loc=d3e3255-108585

+ Details

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

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ntrs_CapitalRequirementsAxis=ntrs_TierIMember
Namespace Prefix:
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Balance Type:
Period Type:

- Details

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Namespace Prefix:
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- Details

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Floating Rate Capital Debt - Additional Information (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended	1 Months Ended
	Dec. 31, 2014	Jan. 31, 1997	Apr. 30, 1997
Tier I \| 2014
Debt Instrument [Line Items]
Phase out of tier capital treatment percentage	50.00%
Tier I \| 2015
Debt Instrument [Line Items]
Phase out of tier capital treatment percentage	25.00%
Tier II \| 2014
Debt Instrument [Line Items]
Phase out of tier capital treatment percentage	50.00%
Tier II \| 2015
Debt Instrument [Line Items]
Phase out of tier capital treatment percentage	75.00%
Tier II \| 2016
Debt Instrument [Line Items]
Phase out of tier capital treatment percentage	60.00%
Tier II \| Thereafter
Debt Instrument [Line Items]
Phase out of tier capital treatment annual incremental percentage	10.00%
NTC Capital I Subordinated Debentures Due January 15th 2027
Debt Instrument [Line Items]
Floating Rate Capital Securities, issued		$ 150
Floating Rate Capital Securities, terms of issue	The Series A Securities were issued at a discount to yield 60.5 basis points above the three-month London Interbank Offered Rate (LIBOR) and are due January 15, 2027. The Series B Securities were issued at a discount to yield 67.9 basis points above the three-month LIBOR and are due April 15, 2027.
Floating Rate Capital Securities, due date	Jan. 15, 2027
Phased out period for tier 1 regulatory capital treatment of securities	3 years
Start date of phased out period for tier 1 regulatory capital treatment of securities	Jan. 01, 2013
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 15th 2027 \| Group One
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate		0.605%
NTC Capital I Subordinated Debentures Due January 15th 2027 \| Group Two
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate		0.52%
NTC Capital II Subordinated Debentures Due April 15th 2027
Debt Instrument [Line Items]
Floating Rate Capital Securities, issued			$ 120
Floating Rate Capital Securities, terms of issue	The Series B Securities were issued at a discount to yield 67.9 basis points above the three-month LIBOR and are due April 15, 2027.
Floating Rate Capital Securities, due date	Apr. 15, 2027
Phased out period for tier 1 regulatory capital treatment of securities	3 years
Start date of phased out period for tier 1 regulatory capital treatment of securities	Jan. 01, 2013
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 15th 2027 \| Group One
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate			0.679%
NTC Capital II Subordinated Debentures Due April 15th 2027 \| Group Two
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate			0.59%