Benefit Plans (Fair Values Of Nonvested Performance Shares And Performance Units) (Details) - $ / shares	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	221,965	257,599	256,566	288,430
Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	76,986	93,320	96,806	116,412
2017 Grant [Member] | Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	63,804
Alliant Energy common stock closing price on March 31, 2017 (in dollars per share)	$ 39.61
Estimated payout percentage based on performance criteria	100.00%
Fair values of each nonvested award (in dollars per share)	$ 39.61
2017 Grant [Member] | Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	21,061
Alliant Energy common stock closing price on March 31, 2017 (in dollars per share)	$ 39.61
Estimated payout percentage based on performance criteria	100.00%
Fair values of each nonvested award (in dollars per share)	$ 39.61
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 March 31, 2017 (in dollars per share)	$ 39.61
Estimated payout percentage based on performance criteria	160.00%
Fair values of each nonvested award (in dollars per share)	$ 63.38
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 March 31, 2017 (in dollars per share)	$ 39.61
Estimated payout percentage based on performance criteria	160.00%
Fair values of each nonvested award (in dollars per share)	$ 63.38
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 March 31, 2017 (in dollars per share)	$ 39.61
Estimated payout percentage based on performance criteria	130.00%
Fair values of each nonvested award (in dollars per share)	$ 51.49
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	130.00%
Fair values of each nonvested award (in dollars per share)	$ 42.32