Common Equity (Common Share Activity) (Details)	3 Months Ended
	Mar. 31, 2012
Common Equity [Abstract]
Shares outstanding, Jan. 1	111,018,821
Equity incentive plans	(5,116)
Other	(51,616)	[1]
Shares outstanding, March 31	110,962,089

[1] Includes shares transferred from employees to Alliant Energy to satisfy tax withholding requirements in connection with the vesting of certain restricted stock under the equity incentive plans.