Benefit Plans (Fair Values Of Nonvested Performance Shares And Units) (Details) - $ / shares	3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	128,283	144,215	144,215	144,424
Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	48,403	58,206	58,564	63,665
2016 Grant [Member] | Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	33,161
Alliant Energy common stock closing price on March 31, 2016 (in dollars per share)	$ 74.28
Estimated payout percentage based on performance criteria	108.00%
Fair values of each nonvested award (in dollars per share)	$ 80.22
2016 Grant [Member] | Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	11,959
Alliant Energy common stock closing price on March 31, 2016 (in dollars per share)	$ 74.28
Estimated payout percentage based on performance criteria	108.00%
Fair values of each nonvested award (in dollars per share)	$ 80.22
2015 Grant [Member] | Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	45,403
Alliant Energy common stock closing price on March 31, 2016 (in dollars per share)	$ 74.28
Estimated payout percentage based on performance criteria	90.00%
Fair values of each nonvested award (in dollars per share)	$ 66.85
2015 Grant [Member] | Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	17,209
Alliant Energy common stock closing price on grant date (in dollars per share)	$ 65.09
Estimated payout percentage based on performance criteria	90.00%
Fair values of each nonvested award (in dollars per share)	$ 58.58
2014 Grant [Member] | Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	49,719
Alliant Energy common stock closing price on March 31, 2016 (in dollars per share)	$ 74.28
Estimated payout percentage based on performance criteria	138.00%
Fair values of each nonvested award (in dollars per share)	$ 102.51
2014 Grant [Member] | Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	19,235
Alliant Energy common stock closing price on grant date (in dollars per share)	$ 53.77
Estimated payout percentage based on performance criteria	138.00%
Fair values of each nonvested award (in dollars per share)	$ 74.20