v2.4.0.6

Benefit Plans (Summary Of Performance Unit Activity) (Details) (Performance Units [Member])	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Performance Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Nonvested, January 1 (in shares/awards)	42,996	[1]	23,128	[1]	0	[1]
Granted (in shares)	24,686	[1]	23,975	[1]	23,795	[1]
Forfeited (in shares)	(2,713)	[1]	(4,107)	[1]	(667)	[1]
Nonvested, December 31 (in shares/awards)	64,969	[1]	42,996	[1]	23,128	[1]
Instrument valuation based on shares of common stock, number of shares	1
Performance multiplier range, lower	0.00%
Performance multiplier range, upper	200.00%
[1] Unit amounts represent the target number of performance units. Each performance unit’s value is based on the average price of one share of Alliant Energy’s common stock on the grant date of the award. The actual payout for performance units is dependent upon actual performance and may range from zero to 200% of the target number of units.

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Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Instrument Valuation Based On Shares of Common Stock, Number of Shares

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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

+ References

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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