Income Taxes (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Income Tax [Line Items]
Net operating loss carryforwards, percentage expiring		99.00%
Scenario, Forecast [Member]
Income Tax [Line Items]
Deductions in income tax return	$ 200
IPL [Member]
Income Tax [Line Items]
Net operating loss carryforwards, percentage expiring		95.00%
IPL [Member] | Scenario, Forecast [Member]
Income Tax [Line Items]
Deductions in income tax return	100
WPL [Member]
Income Tax [Line Items]
Net operating loss carryforwards, percentage expiring		96.00%
WPL [Member] | Scenario, Forecast [Member]
Income Tax [Line Items]
Deductions in income tax return	$ 50