Benefit Plans (Regulatory Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory assets	$ 38.9	$ 37.3
WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory assets	$ 28.1	$ 30.0

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.

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