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://www.xbrl.org/2003/role/presentationRef
-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://www.xbrl.org/2003/role/presentationRef
-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

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

Significant Accounting Policies, Allowance for Funds Used During Construction (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Funds Used During Construction [Abstract]
PPUC approved rate for AFUDC	10.04%	10.04%	10.04%
Minimum [Member]
Allowance for Funds Used During Construction [Abstract]
Allowance for tax-exempt funds rate used during construction			4.00%
Maximum [Member]
Allowance for Funds Used During Construction [Abstract]
Allowance for tax-exempt funds rate used during construction			4.50%