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Risk Management Activities: Utilities (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) MMBTU mW	Dec. 31, 2019 MMBTU mW
Derivative [Line Items]
Collateral Already Posted, Aggregate Fair Value | $	$ 1,500
Natural Gas, Distribution | Future
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	620,000	1,450,000
Derivative, Remaining Maturity	3 months	12 months
Natural Gas, Distribution | Commodity Option
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	3,160,000	3,240,000
Derivative, Remaining Maturity	3 months	3 months
Natural Gas, Distribution | Basis Swap
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	900,000	1,290,000
Derivative, Remaining Maturity	3 months	12 months
Natural Gas, Distribution | Fixed for Float Swaps Purchased
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	3,850,000	4,600,000
Derivative, Remaining Maturity	17 months	24 months
Natural Gas, Distribution | Fixed for Float Swaps Purchased | Cash Flow Hedging | Over the Counter
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	914,600
Natural Gas, Distribution | Natural Gas Physical Purchases
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	17,513,061	13,548,235
Derivative, Remaining Maturity	22 months	12 months
Electricity | Energy Related Derivative
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | mW	219,000	0
Derivative, Remaining Maturity	12 months	0 months

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- Definition

The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4H
-Subparagraph (d)
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+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5580258-113959

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Period remaining until the derivative contract matures, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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