Benefit Plans (Fair Values Of Nonvested Performance Shares And Units) (Details) - $ / shares	9 Months Ended
	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2014
Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	257,599	288,430	288,430	288,848
Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	93,320	116,412	116,412	127,330
2016 Grant [Member] | Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	67,355
Alliant Energy common stock closing price on September 30, 2016 (in dollars per share)	$ 38.31
Estimated payout percentage based on performance criteria	125.00%
Fair values of each nonvested award (in dollars per share)	$ 47.89
2016 Grant [Member] | Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	22,657
Alliant Energy common stock closing price on September 30, 2016 (in dollars per share)	$ 38.31
Estimated payout percentage based on performance criteria	125.00%
Fair values of each nonvested award (in dollars per share)	$ 47.89
2015 Grant [Member] | Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	90,806
Alliant Energy common stock closing price on September 30, 2016 (in dollars per share)	$ 38.31
Estimated payout percentage based on performance criteria	168.00%
Fair values of each nonvested award (in dollars per share)	$ 64.36
2015 Grant [Member] | Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (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	168.00%
Fair values of each nonvested award (in dollars per share)	$ 54.68
2014 Grant [Member] | Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	99,438
Alliant Energy common stock closing price on September 30, 2016 (in dollars per share)	$ 38.31
Estimated payout percentage based on performance criteria	175.00%
Fair values of each nonvested award (in dollars per share)	$ 67.04
2014 Grant [Member] | Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	37,395
Alliant Energy common stock closing price on grant date (in dollars per share)	$ 26.89
Estimated payout percentage based on performance criteria	175.00%
Fair values of each nonvested award (in dollars per share)	$ 47.05