Common Equity (Narrative) (Details) (USD $)	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
IPL [Member]
Common Equity [Line Items]
Retained earnings free of dividend restrictions	$ 430,000,000
Restricted net assets of subsidiaries	1,100,000,000
Capital contributions from parent	60,000,000	50,000,000
Common stock dividends to parent	63,500,000
WPL [Member]
Common Equity [Line Items]
Retained earnings free of dividend restrictions	61,000,000
Restricted net assets of subsidiaries	1,500,000,000
Common stock dividends to parent	$ 58,200,000