Benefit Plans (Fair Values Of Nonvested Performance Shares And Performance Units) (Details) - $ / shares	9 Months Ended
	Sep. 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)	73,240	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 September 29, 2017 (in dollars per share)	$ 41.57
Estimated payout percentage based on performance criteria	100.00%
Fair values of each nonvested award (in dollars per share)	$ 41.57
2017 Grant [Member] | Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards at target (in shares/awards)	19,531
Alliant Energy common stock closing price on September 29, 2017 (in dollars per share)	$ 41.57
Estimated payout percentage based on performance criteria	100.00%
Fair values of each nonvested award (in dollars per share)	$ 41.57
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 September 29, 2017 (in dollars per share)	$ 41.57
Estimated payout percentage based on performance criteria	138.00%
Fair values of each nonvested award (in dollars per share)	$ 57.37
2016 Grant [Member] | Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards at target (in shares/awards)	21,751
Alliant Energy common stock closing price on September 29, 2017 (in dollars per share)	$ 41.57
Estimated payout percentage based on performance criteria	138.00%
Fair values of each nonvested award (in dollars per share)	$ 57.37
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 September 29, 2017 (in dollars per share)	$ 41.57
Estimated payout percentage based on performance criteria	113.00%
Fair values of each nonvested award (in dollars per share)	$ 46.97
2015 Grant [Member] | Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards at target (in shares/awards)	31,958
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