Midcontinent Independent System Operator, Inc. (MISO) (Details 5) - MISO [Member] - Electric transmission rate proceeding [Member] $ in Millions	Sep. 01, 2017 USD ($)
Public Utilities, General Disclosures [Line Items]
Public utilities, requested rate increase (decrease), amount	$ 2.5
Public utilities, approved rate increase (decrease), amount	$ 13.6

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_PublicUtilitiesGeneralDisclosuresLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration