Consideration of Credit Risk and Concentrations (Details) - Credit Concentration Risk $ in Millions	Dec. 31, 2020 USD ($) Counterparty
Derivative [Line Items]
Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure	10
Municipal or Cooperative Entities or Other Utilities
Derivative [Line Items]
Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure	7
External Credit Rating, Investment Grade
Derivative [Line Items]
Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure	4
Wholesale, trading and non trading commodity credit exposure for the most significant counterparties | $	$ 99
Percentage of wholesale, trading and non trading commodity credit exposure for the most significant counterparties	66.00%
No Investment Grade Ratings from External Credit Rating Agencies
Derivative [Line Items]
Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure	4
Wholesale, trading and non trading commodity credit exposure for the most significant counterparties | $	$ 19
Percentage of wholesale, trading and non trading commodity credit exposure for the most significant counterparties	13.00%
External Credit Rating, Non Investment Grade [Member]
Derivative [Line Items]
Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure	2
Wholesale, trading and non trading commodity credit exposure for the most significant counterparties | $	$ 19
Percentage of wholesale, trading and non trading commodity credit exposure for the most significant counterparties	13.00%