Redeemable Preferred Stock Narrative (Details) (USD $) In Millions, except Share data, unless otherwise specified	9 Months Ended	1 Months Ended	9 Months Ended	1 Months Ended			9 Months Ended
	Sep. 30, 2014 IPL [Member]	Mar. 31, 2013 IPL [Member] Redeemable Preferred Stock [Member] 8.375% [Member]	Sep. 30, 2013 Alliant Energy and IPL [Member] Redeemable Preferred Stock [Member]	Mar. 31, 2013 WPL [Member] Redeemable Preferred Stock [Member] 4.40% through 6.50% [Member]	Mar. 31, 2013 WPL [Member] Redeemable Preferred Stock [Member] 4.40% [Member]	Mar. 31, 2013 WPL [Member] Redeemable Preferred Stock [Member] 6.50% [Member]	Sep. 30, 2013 Alliant Energy and WPL [Member] Redeemable Preferred Stock [Member] 4.40% through 6.50% [Member]
Redeemable Preferred Stock [Line Items]
Preferred stock redeemed during period (in shares)		6,000,000		1,049,225
Preferred stock series	5.10%	8.375%			4.40%	6.50%
Preferred stock redeemed during period, value		$ 150		$ 61
Preferred stock redemption charge			$ 5				$ 1