Benefit Plans (Fair Values Of Nonvested Performance Shares And Units) (Details) (USD $)									6 Months Ended
	Jun. 30, 2014 Performance Shares [Member]	Dec. 31, 2013 Performance Shares [Member]	Jun. 30, 2013 Performance Shares [Member]	Dec. 31, 2012 Performance Shares [Member]	Jun. 30, 2014 Performance Units [Member]	Dec. 31, 2013 Performance Units [Member]	Jun. 30, 2013 Performance Units [Member]	Dec. 31, 2012 Performance Units [Member]	Jun. 30, 2014 2014 Grant [Member] Performance Shares [Member]	Jun. 30, 2014 2014 Grant [Member] Performance Units [Member]	Jun. 30, 2014 2013 Grant [Member] Performance Shares [Member]	Jun. 30, 2014 2013 Grant [Member] Performance Units [Member]	Jun. 30, 2014 2012 Grant [Member] Performance Shares [Member]	Jun. 30, 2014 2012 Grant [Member] Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	144,424	139,940	139,940	145,277	64,822	65,912	66,397	64,969	49,719	19,972	49,093	21,726	45,612	23,124
Alliant Energy common stock closing price on June 30, 2014 (in dollars per share)									$ 60.86		$ 60.86		$ 60.86
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									102.00%	102.00%	121.00%	121.00%	126.00%	126.00%
Fair values of each nonvested award (in dollars per share)									$ 62.08	$ 54.85	$ 73.64	$ 57.57	$ 76.68	$ 54.24