Benefit Plans (Fair Values Of Nonvested Performance Shares And Performance Units) (Details) - $ / shares	6 Months Ended
Jun. 30, 2017	Dec. 31, 2016
Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards at target (in shares/awards)	223,511	257,599
Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards at target (in shares/awards)	76,495	93,320
2017 Grant [Member] \| Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards at target (in shares/awards)	65,350
Alliant Energy common stock closing price on June 30, 2017 (in dollars per share)	$ 40.17
Estimated payout percentage based on performance criteria	100.00%
Fair values of each nonvested award (in dollars per share)	$ 40.17
2017 Grant [Member] \| Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards at target (in shares/awards)	20,570
Alliant Energy common stock closing price on June 30, 2017 (in dollars per share)	$ 40.17
Estimated payout percentage based on performance criteria	100.00%
Fair values of each nonvested award (in dollars per share)	$ 40.17
2016 Grant [Member] \| Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards at target (in shares/awards)	67,355
Alliant Energy common stock closing price on June 30, 2017 (in dollars per share)	$ 40.17
Estimated payout percentage based on performance criteria	143.00%
Fair values of each nonvested award (in dollars per share)	$ 57.44
2016 Grant [Member] \| Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards at target (in shares/awards)	22,657
Alliant Energy common stock closing price on June 30, 2017 (in dollars per share)	$ 40.17
Estimated payout percentage based on performance criteria	143.00%
Fair values of each nonvested award (in dollars per share)	$ 57.44
2015 Grant [Member] \| Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards at target (in shares/awards)	90,806
Alliant Energy common stock closing price on June 30, 2017 (in dollars per share)	$ 40.17
Estimated payout percentage based on performance criteria	113.00%
Fair values of each nonvested award (in dollars per share)	$ 45.39
2015 Grant [Member] \| Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards at target (in shares/awards)	33,268
Alliant Energy common stock closing price on grant date (in dollars per share)	$ 32.55
Estimated payout percentage based on performance criteria	113.00%
Fair values of each nonvested award (in dollars per share)	$ 36.78