Commitments and Contingencies, Legal Contingencies (Details)	Jun. 30, 2016 USD ($)
Pacific Northwest FERC Refund Proceeding
Legal Contingencies [Abstract]
Estimated City of Seattle's claim for refunds not including interest	$ 28,000,000
Estimated City of Seattle's Claim for Refunds Including Interest	60,000,000
Accrual for legal contingency	0
Line Extension Disputes
Legal Contingencies [Abstract]
Accrual for legal contingency	0
Minimum \| Pacific Northwest FERC Refund Proceeding
Legal Contingencies [Abstract]
Amount Of Sales Claimed As Subject To Refund	34,000,000
Maximum \| Pacific Northwest FERC Refund Proceeding
Legal Contingencies [Abstract]
Amount Of Sales Claimed As Subject To Refund	$ 50,000,000

Amount of sales claimed by the plaintiff as being subject to refund.

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- Definition

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- Definition

Amount of loss contingency liability.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349

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- Definition

The estimated maximum amount of possible loss from the contingency.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
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- Definition

The estimated minimum amount of possible loss from the contingency.

+ References

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