Summary of Significant Accounting Policies Allowance for Funds Used During Construction (Details)	9 Months Ended	12 Months Ended
Sep. 30, 2017	Dec. 31, 2019	Dec. 31, 2018
Public Utilities, Allowance for Funds Used During Construction, Rate	8.20%	7.60%	7.60%

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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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration