Debt (Narrative) (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024
Line of Credit Facility [Line Items]
Total debt	$ 2,100,000		$ 2,200,000
Long-term debt	1,200,000		1,300,000
Short-term borrowings	0		22,000,000.0
Interest income (expense), net	300,000	$ 500,000
Letters of credit outstanding	9,800,000		9,600,000
Minimum [Member]
Line of Credit Facility [Line Items]
Short-term borrowings	0	0
Maximum [Member]
Line of Credit Facility [Line Items]
Short-term borrowings	37,000,000.0	$ 38,000,000.0
Amended Credit Agreement [Member]
Line of Credit Facility [Line Items]
Remaining borrowing capacity	$ 745,900,000		724,200,000
Credit agreement commitment fee percentage	0.40%
Amended Credit Agreement [Member] | Graybar Canada [Member]
Line of Credit Facility [Line Items]
Letters of credit outstanding	$ 4,100,000		3,800,000
Amended Credit Agreement [Member] | Bridge Loan [Member] | Graybar Canada [Member] | Line of credit [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity	100,000,000.0		100,000,000.0
Amended Credit Agreement [Member] | Bridge Loan [Member] | United States [Member] | Graybar Canada [Member] | Line of credit [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity	75,000,000.0		75,000,000.0
Amended Credit Agreement [Member] | Bridge Loan [Member] | Canada [Member] | Graybar Canada [Member] | Line of credit [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity	20,000,000.0		20,000,000.0
Amended Credit Agreement [Member] | Revolving Credit Facility [Member] | Graybar Canada [Member] | Line of credit [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity	750,000,000.0		750,000,000.0
Accordion feature, increase limit	$ 375,000,000.0		$ 375,000,000.0
Expiration date	Aug. 01, 2026		Aug. 01, 2026
Debt instrument, term	5 years		5 years
Amended Credit Agreement [Member] | Letter of Credit Sub Facility [Member] | Graybar Canada [Member] | Line of credit [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 25,000,000.0		$ 25,000,000.0
Prudential Private Placement Shelf Agreement [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 200,000,000.0
Issuance period	3 years
Notes issued face amount	$ 0		0
MetLife Private Placement Shelf Agreement [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 200,000,000.0
Issuance period	3 years
Notes issued face amount	$ 0		$ 0