Accounting Policies - Derivatives (Details 10) - MMBTU	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Commodity Contract [Member] | Not Designated as Hedging Instrument, Economic Hedge [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure	1,400,000	535,000