Benefit Plans (Fair Values Of Nonvested Performance Shares And Units) (Details) (USD $)									3 Months Ended
	Mar. 31, 2014 Performance Shares [Member]	Dec. 31, 2013 Performance Shares [Member]	Mar. 31, 2013 Performance Shares [Member]	Dec. 31, 2012 Performance Shares [Member]	Mar. 31, 2014 Performance Units [Member]	Dec. 31, 2013 Performance Units [Member]	Mar. 31, 2013 Performance Units [Member]	Dec. 31, 2012 Performance Units [Member]	Mar. 31, 2014 2014 Grant [Member] Performance Shares [Member]	Mar. 31, 2014 2014 Grant [Member] Performance Units [Member]	Mar. 31, 2014 2013 Grant [Member] Performance Shares [Member]	Mar. 31, 2014 2013 Grant [Member] Performance Units [Member]	Mar. 31, 2014 2012 Grant [Member] Performance Shares [Member]	Mar. 31, 2014 2012 Grant [Member] Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	145,926	139,940	139,940	145,277	65,272	65,912	66,397	64,969	51,221	20,422	49,093	21,726	45,612	23,124
Alliant Energy common stock closing price on March 31, 2014 (in dollars per share)									$ 56.81		$ 56.81		$ 56.81
Alliant Energy common stock closing price on grant date (in dollars per share)										$ 53.77		$ 47.58		$ 43.05
Estimated payout percentage based on performance criteria									100.00%	100.00%	118.00%	118.00%	119.00%	119.00%
Fair values of each nonvested award (in dollars per share)									$ 56.81	$ 53.77	$ 67.04	$ 56.14	$ 67.60	$ 51.23