Commitments And Contingencies (Narrative) (Details) (USD $)	1 Months Ended	3 Months Ended						3 Months Ended		3 Months Ended
	Dec. 31, 2010	Mar. 31, 2012	Mar. 31, 2012 IPL [Member]	Mar. 31, 2012 WPL [Member]	Mar. 31, 2012 Manufactured Gas Plant Sites [Member] Alliant Energy Corporation [Member]	Mar. 31, 2012 Manufactured Gas Plant Sites [Member] IPL [Member]	Mar. 31, 2012 Manufactured Gas Plant Sites [Member] WPL [Member]	Mar. 31, 2012 Air Permit Violation Claim [Member] Alliant Energy And WPL [Member]	Dec. 31, 2011 Air Permit Violation Claim [Member] Alliant Energy And WPL [Member]	Mar. 31, 2012 Pension Benefits Costs (Credits) [Member]	Mar. 31, 2012 Mexico [Member]	Mar. 31, 2012 Mexico [Member] Maximum [Member]	Mar. 31, 2012 Performance Guarantees Outstanding, 2012 [Member]	Mar. 31, 2012 Performance Guarantees Outstanding, 2013 [Member]	Mar. 31, 2012 Performance Guarantees Outstanding, 2014 [Member]
Long-term Purchase Commitment [Line Items]
Court stay period for discovery and scheduling deadlines (days)									60
Estimated damages from court opinion and order		$ 17,000,000
Aggregate additional payments to certain plan participants										10,200,000
Indemnification maximum limit												20,000,000
Indemnification expiration date											June 2012
Performance guarantees outstanding		609,000,000											101,000,000	325,000,000	183,000,000
Surety bonds		114,000,000											112,000,000	2,000,000
Present value abandonment obligation		29,000,000
Number of sites with ownership interest			40	14
Number of sites with no further action			11	9
Sites with no further action for soil remediation			3
Minimum remaining estimated cost incurred for investigation, remediation and monitoring		21,000,000	18,000,000	3,000,000
Maximum remaining estimated cost incurred for investigation, remediation and monitoring		45,000,000	41,000,000	4,000,000
Current and non-current environmental liabilities					31,000,000	28,000,000	3,000,000
Interest crediting rate	8.20%
Loss contingency accrual, carrying value, payments		17,000,000
Possible civil penalties per day								$ 37,500