Redeemable Preferred Stock (Narrative) (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended																3 Months Ended	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 IPL [Member] Q board_member	Dec. 31, 2012 IPL [Member]	Dec. 31, 2011 IPL [Member]	Dec. 31, 2013 IPL [Member] Redeemable Preferred Stock [Member] 5.1% [Member]	Dec. 31, 2013 IPL [Member] Redeemable Preferred Stock [Member] 8.375% [Member]	Dec. 31, 2012 IPL [Member] Redeemable Preferred Stock [Member] 8.375% [Member]		Dec. 31, 2013 WPL [Member]	Dec. 31, 2012 WPL [Member]	Dec. 31, 2011 WPL [Member]	Dec. 31, 2013 WPL [Member] Redeemable Preferred Stock [Member] 4.40% [Member]	Dec. 31, 2013 WPL [Member] Redeemable Preferred Stock [Member] 6.50% [Member]	Dec. 31, 2013 Alliant Energy and IPL [Member] Redeemable Preferred Stock [Member] 5.1% [Member]	Mar. 31, 2013 Long-term debt [Member]	Dec. 31, 2013 Long-term debt [Member] IPL [Member] Redeemable Preferred Stock [Member] 5.1% [Member]	Dec. 31, 2013 Minimum [Member] WPL [Member]		Dec. 31, 2013 Maximum [Member] WPL [Member]
Temporary Equity [Line Items]
Preferred stock issued during period (in shares)							8,000,000
Cumulative preferred stock rate				5.10%	8.375%		5.10%	8.375%	8.375%	[1]		4.50%		4.40%	6.50%				4.40%	[2]	6.50%	[2]
Preferred stock issued during period, value							$ 200
Reduction in commercial paper	11.9	164.7	55.4	(76.3)	69.2	7.1					97.1	60.9	(21.7)				65.0	40.0
Preferred stock issuance costs	$ (5.4)			$ (5.4)												$ 5.0
Number of board members to be elected (in members)				2
Number of quarterly dividend requirements (in quarters)				6

[1] In 2013, IPL redeemed all 6,000,000 outstanding shares of its 8.375% cumulative preferred stock for $150 million plus accrued and unpaid dividends to the redemption date. Alliant Energy and IPL recorded a $5 million charge in 2013 related to this transaction in “Preferred dividend requirements” in their Consolidated Statements of Income.

[2] In 2013, WPL redeemed all 1,049,225 outstanding shares of its 4.40% through 6.50% cumulative preferred stock for $61 million plus accrued and unpaid dividends to the redemption date. Alliant Energy and WPL recorded a $1 million charge in 2013 related to this transaction in “Preferred dividend requirements” in their Consolidated Statements of Income.