| Regulatory deferral account debit balances | en | http://www.xbrl.org/2003/role/label | http://www.xbrl.org/2003/role/link |
| Total regulatory deferral account debit balances | en | http://www.xbrl.org/2003/role/totalLabel | http://www.xbrl.org/2003/role/link |
| Regulatory deferral account debit balances at beginning of period | en | http://www.xbrl.org/2003/role/periodStartLabel | http://www.xbrl.org/2003/role/link |
| Regulatory deferral account debit balances at end of period | en | http://www.xbrl.org/2003/role/periodEndLabel | http://www.xbrl.org/2003/role/link |