Derivative Accounting - Outstanding Gross Notional Amounts Outstanding (Details) - Commodity Contracts MMcf in Thousands	12 Months Ended
Dec. 31, 2016 GWh MMcf
Outstanding gross notional amount of derivatives
Power \| GWh	1,314
Gas \| MMcf	194

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