| Remaining reversal period of regulatory deferral account credit balances | en | http://www.xbrl.org/2003/role/label | http://www.xbrl.org/2003/role/link |
| Concept not required as a result of 2018 annual improvements | en | http://www.xbrl.org/2009/role/deprecatedLabel | http://www.xbrl.org/2003/role/link |
| 2019-01-01 | en | http://www.xbrl.org/2009/role/deprecatedDateLabel | http://www.xbrl.org/2003/role/link |
| The remaining reversal period of regulatory deferral account credit balances. [Refer: Regulatory deferral account credit balances] | en | http://www.xbrl.org/2003/role/documentation | http://www.xbrl.org/2003/role/link |