Risk Management Counterparties Representing 10% or More of Assets and Liabilities from price risk management activities (Details)	Sep. 30, 2021	Dec. 31, 2020
Assets from price risk management activities:
Counterparty A	13.00%	12.00%
Counterparty B	12.00%	17.00%
Counterparty C	27.00%	21.00%
Counterparty D	8.00%	16.00%
Fair Value, Concentration of Risk, Trading Account Assets	0.11	0.08
Counterparty F	0.12	0.05
Concentration of Risk, Derivative Instruments, Assets	83.00%	79.00%
Counterparty G	0.69	0.93
Counterparty H	0.11	0
Liabilities from price risk management activities:
Counterparty E	80.00%	93.00%