Common Equity (Narrative) (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule of Common Equity [Line Items]
Shares available for issuance under the OIP, Shareowner Direct Plan and 401(k) Savings Plan	7,800,000
Ownership percentage	15.00%
Initial right entitlement, number of shares of common stock shareholders have the option to purchase (in shares)	0.5
Exercise price, rights (in dollars per share)	$ 110
Percentage of exercise price upon change in beneficial ownership	200.00%
Other comprehensive income (loss)	$ (0.4)	$ 0.6	$ 0
IPL [Member]
Schedule of Common Equity [Line Items]
Common equity ratio, computation of ratio average, number of months	13 months
Common equity ratio	42.00%
Retained earnings free of dividend restrictions	538
Other comprehensive income (loss)	0	0	0
WPL [Member]
Schedule of Common Equity [Line Items]
Common equity ratio, computation of ratio average, number of months	13 months
Retained earnings free of dividend restrictions	127
Other comprehensive income (loss)	0	0	0
Minimum [Member]
Schedule of Common Equity [Line Items]
Ownership percentage	10.00%
2015 [Member] | WPL [Member]
Schedule of Common Equity [Line Items]
Common equity ratio	51.79%
Retained earnings free of dividend restrictions	127
2016 [Member] | WPL [Member]
Schedule of Common Equity [Line Items]
Common equity ratio	52.25%
Retained earnings free of dividend restrictions	$ 135