Commitments and Contingencies Line Extension Disputes (Details) - Line Extension Disputes [Member] - Minimum [Member] $ in Millions	1 Months Ended
Dec. 31, 2015	Mar. 31, 2019 USD ($)
Loss Contingencies [Line Items]
Loss Contingency, Number of Plaintiffs	50
PSCo [Member]
Loss Contingencies [Line Items]
Loss Contingency Accrual		$ 0.0

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=118942415&loc=d3e14326-108349

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