Commitments and Contingencies, Legal Contingencies (Details) - PSCo [Member] - Minimum - Line Extension Disputes	1 Months Ended
Dec. 31, 2015	Dec. 31, 2018 USD ($)
Legal Contingencies [Abstract]
Loss Contingency, Number of Plaintiffs	50
Accrual For Legal Contingency		$ 0

Amount of loss contingency liability.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14326-108349

Name:	us-gaap_LossContingencyAccrualAtCarryingValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant