Benefit Plans (Summary Of Performance Unit Activity) (Details) (Performance Units [Member], USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
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)	64,969	[1]	42,996	[1]	23,128	[1]
Granted (in shares/awards)	22,201	[1]	24,686	[1]	23,975	[1]
Vested (in shares/awards)	(19,760)	[1],[2]	0	[1],[2]	0	[1],[2]
Forfeited (in shares/awards)	(1,498)	[1]	(2,713)	[1]	(4,107)	[1]
Nonvested, December 31 (in shares/awards)	65,912	[1]	64,969	[1]	42,996	[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%
Vested percentage of the target	197.50%
Cash payout value	$ 1.3

[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.

[2] In 2013, 19,760 performance units granted in 2010 vested at 197.5% of the target, resulting in cash payouts valued at $1.3 million