| 有形固定資産 | ja | http://www.xbrl.org/2003/role/label | http://www.xbrl.org/2003/role/link |
| 有形固定資産、その他の固定資産、高速道路事業 | ja | http://www.xbrl.org/2003/role/verboseLabel | http://www.xbrl.org/2003/role/link |
| 有形固定資産合計 | ja | http://www.xbrl.org/2003/role/totalLabel | http://www.xbrl.org/2003/role/link |
| Property, plant and equipment | en | http://www.xbrl.org/2003/role/label | http://www.xbrl.org/2003/role/link |
| Property, plant and equipment-other noncurrent assets-HWY | en | http://www.xbrl.org/2003/role/verboseLabel | http://www.xbrl.org/2003/role/link |
| Total property, plant and equipment | en | http://www.xbrl.org/2003/role/totalLabel | http://www.xbrl.org/2003/role/link |