Derivative Accounting - Schedule of Gross Notional Amounts Outstanding (Details) - Commodity Contracts GWh in Thousands, Bcf in Thousands	Sep. 30, 2019 GWh Bcf	Dec. 31, 2018 GWh Bcf
Outstanding gross notional amount of derivatives
Power \| GWh	232	250
Gas \| Bcf	187	218

Nominal energy measure used to calculate payments on a derivative instrument.

No definition available.

Name:	us-gaap_DerivativeNonmonetaryNotionalAmountEnergyMeasure
Namespace Prefix:	us-gaap_
Data Type:	num:energyItemType
Balance Type:	na
Period Type:	duration