Common Equity (Common Share Activity) (Details)	6 Months Ended
	Jun. 30, 2012
Common Stock Oustanding [Roll Forward]
Shares outstanding, Jan. 1 (in shares)	111,018,821
Equity incentive plans (in shares)	8,937
Other (in shares)	(51,616)	[1]
Shares outstanding, June 30 (in shares)	110,976,142

[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.