Selected Balance Sheet Data, Inventory (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Public Utilities, Inventory [Line Items]
Inventories	$ 14.0	$ 17.1
Materials and supplies
Public Utilities, Inventory [Line Items]
Inventories	7.1	6.7
Fuel
Public Utilities, Inventory [Line Items]
Inventories	3.8	3.8
Natural gas
Public Utilities, Inventory [Line Items]
Inventories	$ 3.1	$ 6.6

The period end amount for a type of inventory held by the utility in a schedule of inventories.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(6)(a))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_PublicUtilitiesInventory
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant