Redeemable Preferred Stock (Carrying Value Of Cumulative Preferred Stock) (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012
Temporary Equity [Line Items]
Cumulative preferred stock	$ 200.0		$ 145.1
Cumulative preferred stock	0		60.0
Redeemable Preferred Stock [Member]
Temporary Equity [Line Items]
Cumulative preferred stock	200.0		205.1
IPL [Member]
Temporary Equity [Line Items]
Authorized shares (in shares)	16,000,000		16,000,000
Cumulative preferred stock rate	5.10%		8.375%
Cumulative preferred stock	200.0		145.1
IPL [Member] | Redeemable Preferred Stock [Member]
Temporary Equity [Line Items]
Cumulative preferred stock	200.0		145.1
Less: discount	0		(4.9)
WPL [Member]
Temporary Equity [Line Items]
Authorized shares (in shares)	16,000,000		3,750,000
Cumulative preferred stock rate			4.50%
Cumulative preferred stock	0		60.0
5.1% [Member] | IPL [Member] | Redeemable Preferred Stock [Member]
Temporary Equity [Line Items]
Liquidation Preference/Stated Value (in dollars per share)	$ 25
Shares outstanding (in shares)	8,000,000
Cumulative preferred stock rate	5.10%
Redemption (none are mandatorily redeemable)	On or after March 15, 2018
Cumulative preferred stock	200.0		0
8.375% [Member] | IPL [Member] | Redeemable Preferred Stock [Member]
Temporary Equity [Line Items]
Liquidation Preference/Stated Value (in dollars per share)			$ 25	[1]
Shares outstanding (in shares)			6,000,000	[1]
Cumulative preferred stock rate	8.375%		8.375%	[1]
Cumulative preferred stock	0	[1]	150.0	[1]
Preferred stock redeemed during period (in shares)	6,000,000
Preferred stock redeemed during period, value	150
8.375% [Member] | Alliant Energy and IPL [Member] | Redeemable Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred stock redemption charge	5
4.40% through 6.50% [Member] | WPL [Member] | Redeemable Preferred Stock [Member]
Temporary Equity [Line Items]
Shares outstanding (in shares)			1,049,225	[2]
Cumulative preferred stock	0	[2]	60.0	[2]
Preferred stock redeemed during period (in shares)	1,049,225
Preferred stock redeemed during period, value	61
4.40% through 6.50% [Member] | Alliant Energy and WPL [Member] | Redeemable Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred stock redemption charge	$ 1
Maximum [Member] | WPL [Member]
Temporary Equity [Line Items]
Liquidation Preference/Stated Value (in dollars per share)			$ 100	[2]
Cumulative preferred stock rate	6.50%	[2]
Minimum [Member] | WPL [Member]
Temporary Equity [Line Items]
Liquidation Preference/Stated Value (in dollars per share)			$ 25	[2]
Cumulative preferred stock rate	4.40%	[2]

[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.