Line of Credit Facility, Accordion Feature, Increase Limit

No definition available.

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- Definition

Long-Term Debt, Fair Value, Fixed Rate Debt Carrying Amount in Excess of Fair Value

+ References

No definition available.

+ Details

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Period Type:	instant

- 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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Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Section 55
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-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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Period Type:	duration

- Definition

Amount of unused borrowing capacity under the long-term financing arrangement that is available to the entity as of the balance sheet date.

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of the cost of borrowed funds accounted for as interest expense for debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6036836-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.8)
-URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227

+ Details

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

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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

- Definition

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

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

- 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

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

+ References

Reference 1: 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(19)(a))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 210
-Section S99
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-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

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-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Weighted average interest rate of short-term debt outstanding calculated at point in time.

+ References

+ Details

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

- Definition

For the form of debt having an initial term of less than one year or less than the normal operating cycle, if longer, average borrowings during the period.

+ References

No definition available.

+ Details

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

- Definition

Unused amount of commitments to extend credit to customers.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

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- Details

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- Details

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Debt (Narrative) (Details) - USD ($)		12 Months Ended
Debt (Narrative) (Details) - USD ($)	Aug. 10, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Line of Credit Facility [Line Items]
Fixed rate debt carrying amount in excess of fair value		$ 1,400,000	$ 1,500,000
Short-term borrowings		$ 138,000,000.0	235,000,000.0
Revolving Credit Facility
Line of Credit Facility [Line Items]
Weighted average interest rate		2.78%
Letter of Credit
Line of Credit Facility [Line Items]
Letters of credit outstanding		$ 5,600,000	5,600,000
Credit Agreement [Member] \| Revolving Credit Facility
Line of Credit Facility [Line Items]
Remaining borrowing capacity		611,500,000	515,000,000.0
Short-term borrowings		138,000,000.0	235,000,000.0
Short-term debt average amount outstanding		$ 151,000,000.0	$ 202,000,000.0
Weighted average interest rate		3.42%	3.05%
Debt instrument interest expense		$ 5,500,000	$ 6,900,000	$ 4,200,000
Credit Agreement [Member] \| Revolving Credit Facility \| Minimum
Line of Credit Facility [Line Items]
Short-term borrowings		10,000,000.0	140,000,000.0
Credit Agreement [Member] \| Revolving Credit Facility \| Maximum
Line of Credit Facility [Line Items]
Short-term borrowings		$ 257,000,000.0	261,000,000.0
Amended Credit Agreement
Line of Credit Facility [Line Items]
Debt Instrument, Term		5 years
Letters of credit outstanding		$ 500,000	0
Prudential Private Placement Shelf Agreement
Line of Credit Facility [Line Items]
Agreement face amount		100,000,000.0
Notes issued face amount		0	0
MetLife Private Placement Shelf Agreement
Line of Credit Facility [Line Items]
Agreement face amount		100,000,000.0
Notes issued face amount		$ 0	$ 0
Line of credit \| Revolving Credit Facility \| Graybar Canada [Member] \| Minimum \| Base Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.00%
Line of credit \| Revolving Credit Facility \| Graybar Canada [Member] \| Maximum \| Base Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.60%
Line of credit \| Credit Agreement [Member] \| Bridge Loan \| UNITED STATES
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 75,000,000.0
Line of credit \| Amended Credit Agreement
Line of Credit Facility [Line Items]
Maximum borrowing capacity	750,000,000.0
Line of credit \| Amended Credit Agreement \| Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of Credit Facility, Accordion Feature, Increase Limit	$ 375,000,000.0
Line of credit \| Amended Credit Agreement \| Revolving Credit Facility \| Minimum
Line of Credit Facility [Line Items]
Credit agreement commitment fee percentage	0.25%
Line of credit \| Amended Credit Agreement \| Revolving Credit Facility \| Minimum \| Base Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.00%
Line of credit \| Amended Credit Agreement \| Revolving Credit Facility \| Minimum \| London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.00%
Line of credit \| Amended Credit Agreement \| Revolving Credit Facility \| Maximum
Line of Credit Facility [Line Items]
Credit agreement commitment fee percentage	0.40%
Line of credit \| Amended Credit Agreement \| Revolving Credit Facility \| Maximum \| Base Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.60%
Line of credit \| Amended Credit Agreement \| Revolving Credit Facility \| Maximum \| London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.60%
Line of credit \| Amended Credit Agreement \| Revolving Credit Facility \| Graybar Canada [Member] \| Minimum \| CDOR [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.00%
Line of credit \| Amended Credit Agreement \| Revolving Credit Facility \| Graybar Canada [Member] \| Maximum \| CDOR [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.60%
Line of credit \| Amended Credit Agreement \| Letter of Credit Sub-Facility [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 25,000,000.0
Line of credit \| Amended Credit Agreement \| Bridge Loan \| Graybar Canada [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity	100,000,000.0
Line of credit \| Amended Credit Agreement \| Bridge Loan \| CANADA
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 20,000,000.0
Line of credit \| Amended Credit Agreement \| Letter of Credit \| Minimum
Line of Credit Facility [Line Items]
Credit agreement commitment fee percentage	1.00%
Line of credit \| Amended Credit Agreement \| Letter of Credit \| Maximum
Line of Credit Facility [Line Items]
Credit agreement commitment fee percentage	1.60%