Summary of Significant Accounting Policies Allowance for Funds Used During Construction (Details)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Public Utilities, Allowance for Funds Used During Construction, Rate	7.60%	8.20%	8.20%

Effective rate, including composite rate, of cost of financing additions to qualifying regulated assets, commonly called allowance for funds used during construction.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 835
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6501662&loc=d3e56162-110433

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 835
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6501569&loc=d3e55921-110430

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration