Benefit Plans (Fair Values Of Nonvested Performance Shares And Units) (Details) - $ / shares		6 Months Ended
		Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Dec. 31, 2013
Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	[1]	144,215	144,424	144,424	139,940
Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	[2]	58,324	63,665	64,822	65,912
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 June 30, 2015 (in dollars per share)		$ 57.72
Estimated payout percentage based on performance criteria		100.00%
Fair values of each nonvested award (in dollars per share)		$ 57.72
2015 Grant [Member] | Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)		17,504
Alliant Energy common stock closing price on grant date (in dollars per share)		$ 65.09
Estimated payout percentage based on performance criteria		100.00%
Fair values of each nonvested award (in dollars per share)		$ 65.09
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 June 30, 2015 (in dollars per share)		$ 57.72
Estimated payout percentage based on performance criteria		133.00%
Fair values of each nonvested award (in dollars per share)		$ 76.77
2014 Grant [Member] | Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)		19,440
Alliant Energy common stock closing price on grant date (in dollars per share)		$ 53.77
Estimated payout percentage based on performance criteria		133.00%
Fair values of each nonvested award (in dollars per share)		$ 71.51
2013 Grant [Member] | Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)		49,093
Alliant Energy common stock closing price on June 30, 2015 (in dollars per share)		$ 57.72
Estimated payout percentage based on performance criteria		180.00%
Fair values of each nonvested award (in dollars per share)		$ 103.90
2013 Grant [Member] | Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)		21,380
Alliant Energy common stock closing price on grant date (in dollars per share)		$ 47.58
Estimated payout percentage based on performance criteria		180.00%
Fair values of each nonvested award (in dollars per share)		$ 85.64

[1] Share amounts represent the target number of performance shares.

[2] Unit amounts represent the target number of performance units.