| Pay vs Performance Disclosure - USD ($) | 12 Months Ended |
| Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020 |
| Pay vs Performance Disclosure | | | | |
| Pay vs Performance Disclosure, Table | Value of Initial Fixed $100 Investment Based On: Fiscal Summary Compensation Table Total for PEO (1) (2) ($) Compensation Actually Paid to PEO (1) (2) ($) Average Summary Compensation Table Total for Other NEOs (1) (2) ($) Average Compensation Actually Paid to Other NEOs (1) (2) ($) FAST Total Shareholder Return (3) ($) Peer Group Total Shareholder Return (3) (4) Net Income (5) ($ in millions) Company-Wide Pre-Tax Earnings (6) ($ in millions) 2023 3,115,507 5,360,613 1,449,743 1,757,205 196 218 1,155.0 1,522.0 2022 5,439,610 3,307,940 2,408,942 1,793,142 138 147 1,086.9 1,440.0 2021 2,423,614 5,572,876 1,358,039 2,295,107 183 169 925.0 1,207.8 2020 2,539,150 5,321,725 1,316,849 2,067,665 137 126 859.1 1,132.7 | | | |
| Company Selected Measure Name | company-wide pre-tax earnings | | | |
| Named Executive Officers, Footnote | Our PEO and Other NEOs for each reported fiscal year were: Fiscal PEO Other NEOs 2023 Daniel L. Florness Holden Lewis, Charles S. Miller, Jeffery M. Watts, John L. Soderberg, and Terry M. Owen (i) 2022 Daniel L. Florness Holden Lewis, Terry M. Owen, Charles S. Miller, and Reyne K. Wisecup 2021 Daniel L. Florness Holden Lewis, Jeffery M. Watts, Terry M. Owen, and William J. Drazkowski 2020 Daniel L. Florness Holden Lewis, Terry M. Owen, Jeffery M. Watts, and Reyne K. Wisecup (i) Mr. Owen resigned on October 31, 2023. | | | |
| Changed Peer Group, Footnote | Our peer group used for the TSR calculation is the Dow Jones US Industrial Suppliers Index, which is the industry index used to show our performance in our Form 10-K. In our pay versus performance disclosures for 2022, we used the S&P 500. Pursuant to SEC guidance, we have changed the index used for our peer group. A comparison of our TSR, the S&P 500 TSR, and the Dow Jones US Industrial Suppliers Index TSR is below: TSR FAST S&P 500 Dow Jones US 2023 196 158 218 2022 138 125 147 2021 183 152 169 2020 137 118 126 | | | |
| PEO Total Compensation Amount | $ 3,115,507 | $ 5,439,610 | $ 2,423,614 | $ 2,539,150 |
| PEO Actually Paid Compensation Amount | $ 5,360,613 | 3,307,940 | 5,572,876 | 5,321,725 |
| Adjustment To PEO Compensation, Footnote | SEC rules require certain adjustments be made to the Summary Compensation Table (SCT) totals to determine 'compensation actually paid' (CAP) as reported in the Pay Versus Performance Table. CAP does not necessarily represent cash and/or equity value transferred to the applicable NEO without restriction, but rather is a value calculated under applicable SEC rules. The PEO and NEOs do not participate in a defined benefit plan, so no adjustment for pension benefits is included in the table below. The following table details these adjustments from the SCT total compensation to determine CAP in 2023: Adjustments PEO Average of Other NEOs Total Compensation from SCT 3,115,507 1,449,743 Adjustments for Stock and Option Awards Subtract SCT amounts of stock and option awards (847,284) (289,652) Add fair value as of the year-end of awards granted during 2023 that are outstanding and unvested at the end of 2023 1,691,588 433,290 Plus (Minus) change in fair value of awards between the end of 2022 and the end of 2023 for awards granted in any prior fiscal year that are outstanding and unvested at the end of 2023 1,393,590 269,996 Add vesting date fair value of awards granted and vesting during 2023 — — Plus (Minus) change in fair value from the end of 2022 to the vesting date of awards granted in any prior fiscal year which met all vesting conditions during 2023 7,212 4,134 Subtract fair value at end of 2022 for awards granted in any prior fiscal year that fail to meet the applicable vesting conditions during 2023 — (110,306) Add dividends or other earnings paid on stock or option awards in 2023 prior to vesting if not otherwise included in the SCT for the covered year — — Compensation Actually Paid (as calculated) 5,360,613 1,757,205 | | | |
| Non-PEO NEO Average Total Compensation Amount | $ 1,449,743 | 2,408,942 | 1,358,039 | 1,316,849 |
| Non-PEO NEO Average Compensation Actually Paid Amount | $ 1,757,205 | 1,793,142 | 2,295,107 | 2,067,665 |
| Adjustment to Non-PEO NEO Compensation Footnote | SEC rules require certain adjustments be made to the Summary Compensation Table (SCT) totals to determine 'compensation actually paid' (CAP) as reported in the Pay Versus Performance Table. CAP does not necessarily represent cash and/or equity value transferred to the applicable NEO without restriction, but rather is a value calculated under applicable SEC rules. The PEO and NEOs do not participate in a defined benefit plan, so no adjustment for pension benefits is included in the table below. The following table details these adjustments from the SCT total compensation to determine CAP in 2023: Adjustments PEO Average of Other NEOs Total Compensation from SCT 3,115,507 1,449,743 Adjustments for Stock and Option Awards Subtract SCT amounts of stock and option awards (847,284) (289,652) Add fair value as of the year-end of awards granted during 2023 that are outstanding and unvested at the end of 2023 1,691,588 433,290 Plus (Minus) change in fair value of awards between the end of 2022 and the end of 2023 for awards granted in any prior fiscal year that are outstanding and unvested at the end of 2023 1,393,590 269,996 Add vesting date fair value of awards granted and vesting during 2023 — — Plus (Minus) change in fair value from the end of 2022 to the vesting date of awards granted in any prior fiscal year which met all vesting conditions during 2023 7,212 4,134 Subtract fair value at end of 2022 for awards granted in any prior fiscal year that fail to meet the applicable vesting conditions during 2023 — (110,306) Add dividends or other earnings paid on stock or option awards in 2023 prior to vesting if not otherwise included in the SCT for the covered year — — Compensation Actually Paid (as calculated) 5,360,613 1,757,205 | | | |
| Compensation Actually Paid vs. Total Shareholder Return | CAP Versus Company and Peer Group TSR (1) | | | |
| Compensation Actually Paid vs. Net Income | CAP Versus Net Income and Company-Wide Pre-Tax Earnings | | | |
| Compensation Actually Paid vs. Company Selected Measure | CAP Versus Net Income and Company-Wide Pre-Tax Earnings | | | |
| Tabular List, Table | The following table lists the most important financial performance measures we used to link CAP to the NEOs for fiscal 2023 to our performance: PEO CFO Other NEOs Company-wide pre-tax earnings Company-wide pre-tax earnings Company-wide pre-tax earnings Working capital management Company-wide net income Working capital management Working capital management | | | |
| Total Shareholder Return Amount | $ 196 | 138 | 183 | 137 |
| Peer Group Total Shareholder Return Amount | 218 | 147 | 169 | 126 |
| Net Income (Loss) | $ 1,155,000,000 | $ 1,086,900,000 | $ 925,000,000 | $ 859,100,000 |
| Company Selected Measure Amount | 1,522,000,000 | 1,440,000,000 | 1,207,800,000 | 1,132,700,000 |
| PEO Name | Daniel L. Florness | Daniel L. Florness | Daniel L. Florness | Daniel L. Florness |
| Peer Group Total Shareholder Return Amount, Prior | $ 158 | $ 125 | $ 152 | $ 118 |
| Measure:: 4 | | | | |
| Pay vs Performance Disclosure | | | | |
| Other Performance Measure, Amount | 100 | | | |
| Non-GAAP Measure Description | Total shareholder return is calculated based on a fixed investment of one hundred dollars measured from the market close on December 31, 2019 (the last trading day of the fiscal 2019) through and including the end of each fiscal year reported in the table. | | | |
| Measure:: 5 | | | | |
| Pay vs Performance Disclosure | | | | |
| Non-GAAP Measure Description | The "net earnings" line item in our consolidated statements of earnings is equal to both "net income" and "company-wide net income," and is calculated in conformity with U.S. GAAP. | | | |
| Measure:: 6 | | | | |
| Pay vs Performance Disclosure | | | | |
| Non-GAAP Measure Description | Our company-selected measure, which is the measure we believe represents the most important financial performance not otherwise presented in the table above that we use to link CAP to our NEOs for fiscal 2023 to our company's performance, is company-wide pre-tax earnings. The "earnings before income taxes" line item in our consolidated statements of earnings is equal to "company-wide pre-tax earnings" and is calculated in conformity with U.S. GAAP. | | | |
| PEO | Measure:: 1 | | | | |
| Pay vs Performance Disclosure | | | | |
| Name | Company-wide pre-tax earnings | | | |
| PEO | Measure:: 2 | | | | |
| Pay vs Performance Disclosure | | | | |
| Name | Working capital management | | | |
| PEO | Equity Awards, Subtract SCT amounts of stock and option awards [Member] | | | | |
| Pay vs Performance Disclosure | | | | |
| Adjustment to Compensation, Amount | $ (847,284) | | | |
| PEO | Equity Awards, Add fair value as of the year-end of awards granted during fiscal year that are outstanding and unvested at the end of fiscal year [Member] | | | | |
| Pay vs Performance Disclosure | | | | |
| Adjustment to Compensation, Amount | 1,691,588 | | | |
| PEO | Equity Awards, Plus (Minus) change in fair value of awards between the end of 2022 and the end of 2023 for awards granted in any prior fiscal year that are outstanding and unvested at the end of 2023 [Member] | | | | |
| Pay vs Performance Disclosure | | | | |
| Adjustment to Compensation, Amount | 1,393,590 | | | |
| PEO | Equity Awards, Add vesting date fair value of awards granted and vesting during fiscal year [Member] | | | | |
| Pay vs Performance Disclosure | | | | |
| Adjustment to Compensation, Amount | 0 | | | |
| PEO | Equity Awards, Plus (Minus) change in fair value from the end of 2022 to the vesting date of awards granted in any prior fiscal year which met all vesting conditions during 2023 [Member] | | | | |
| Pay vs Performance Disclosure | | | | |
| Adjustment to Compensation, Amount | 7,212 | | | |
| PEO | Equity Awards, Subtract fair value at end of 2022 for awards granted in any prior fiscal year that fail to meet the applicable vesting conditions during fiscal year [Member] | | | | |
| Pay vs Performance Disclosure | | | | |
| Adjustment to Compensation, Amount | 0 | | | |
| PEO | Equity Awards, Add dividends or other earnings paid on stock or option awards in fiscal year prior to vesting if not otherwise included in the SCT for the covered year [Member] | | | | |
| Pay vs Performance Disclosure | | | | |
| Adjustment to Compensation, Amount | $ 0 | | | |
| Non-PEO NEO | Measure:: 1 | | | | |
| Pay vs Performance Disclosure | | | | |
| Name | Company-wide pre-tax earnings | | | |
| Non-PEO NEO | Measure:: 2 | | | | |
| Pay vs Performance Disclosure | | | | |
| Name | Working capital management | | | |
| Non-PEO NEO | Equity Awards, Subtract SCT amounts of stock and option awards [Member] | | | | |
| Pay vs Performance Disclosure | | | | |
| Adjustment to Compensation, Amount | $ (289,652) | | | |
| Non-PEO NEO | Equity Awards, Add fair value as of the year-end of awards granted during fiscal year that are outstanding and unvested at the end of fiscal year [Member] | | | | |
| Pay vs Performance Disclosure | | | | |
| Adjustment to Compensation, Amount | 433,290 | | | |
| Non-PEO NEO | Equity Awards, Plus (Minus) change in fair value of awards between the end of 2022 and the end of 2023 for awards granted in any prior fiscal year that are outstanding and unvested at the end of 2023 [Member] | | | | |
| Pay vs Performance Disclosure | | | | |
| Adjustment to Compensation, Amount | 269,996 | | | |
| Non-PEO NEO | Equity Awards, Add vesting date fair value of awards granted and vesting during fiscal year [Member] | | | | |
| Pay vs Performance Disclosure | | | | |
| Adjustment to Compensation, Amount | 0 | | | |
| Non-PEO NEO | Equity Awards, Plus (Minus) change in fair value from the end of 2022 to the vesting date of awards granted in any prior fiscal year which met all vesting conditions during 2023 [Member] | | | | |
| Pay vs Performance Disclosure | | | | |
| Adjustment to Compensation, Amount | 4,134 | | | |
| Non-PEO NEO | Equity Awards, Subtract fair value at end of 2022 for awards granted in any prior fiscal year that fail to meet the applicable vesting conditions during fiscal year [Member] | | | | |
| Pay vs Performance Disclosure | | | | |
| Adjustment to Compensation, Amount | (110,306) | | | |
| Non-PEO NEO | Equity Awards, Add dividends or other earnings paid on stock or option awards in fiscal year prior to vesting if not otherwise included in the SCT for the covered year [Member] | | | | |
| Pay vs Performance Disclosure | | | | |
| Adjustment to Compensation, Amount | $ 0 | | | |
| CFO [Member] | Measure:: 1 | | | | |
| Pay vs Performance Disclosure | | | | |
| Name | Company-wide pre-tax earnings | | | |
| CFO [Member] | Measure:: 2 | | | | |
| Pay vs Performance Disclosure | | | | |
| Name | Working capital management | | | |
| CFO [Member] | Measure:: 3 | | | | |
| Pay vs Performance Disclosure | | | | |
| Name | Company-wide net income | | | |
