Commitments And Contingencies (Narrative) ( Details) (USD $)	1 Months Ended	3 Months Ended		9 Months Ended				3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended		6 Months Ended	9 Months Ended								12 Months Ended	3 Months Ended	9 Months Ended			3 Months Ended
	Sep. 30, 2011	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011 mW	Sep. 30, 2010	Sep. 30, 2011 Maximum [Member]	Sep. 30, 2011 Minimum [Member]	Sep. 30, 2011 IPL [Member] Defined Benefit Pension Plans [Member]	Sep. 30, 2011 IPL [Member] Defined Benefit Pension Plans [Member]	Sep. 30, 2011 WPL [Member] Defined Benefit Pension Plans [Member]	Sep. 30, 2011 WPL [Member] Defined Benefit Pension Plans [Member]	Sep. 30, 2011 Defined Benefit Pension Plans [Member]		Dec. 31, 2011 Defined Benefit Pension Plans [Member]	Sep. 30, 2011 Defined Benefit Pension Plans [Member]		Sep. 30, 2011 Alliant Energy And WPL [Member] Air Permit Violation Claim [Member]	Sep. 30, 2011 Wind Project [Member]	Sep. 30, 2011 Alliant Energy Corporation [Member] SO2 Emission Allowances [Member]		Sep. 30, 2011 IPL [Member] SO2 Emission Allowances [Member]		Dec. 31, 2007 IPL [Member] SO2 Emission Allowances [Member]	Sep. 30, 2011 SO2 Emission Allowances [Member] Alliant Energy And IPL [Member]	Sep. 30, 2011 Alliant Energy Corporation [Member]	Sep. 30, 2011 IPL [Member]	Sep. 30, 2011 WPL [Member]	Sep. 30, 2011 RMT [Member]
Wind turbine generator set capacity				500
Minimum future commitments																		$ 19,000,000	$ 34,000,000	[1]	$ 34,000,000	[1]	$ 34,000,000	$ 34,000,000	$ 1,484,000,000	$ 790,000,000	$ 471,000,000
Possible civil penalties per day																	37,500
Interest crediting rate				8.20%
Estimated damages from court opinion and order				6,000,000
Aggregate additional payments to certain plan participants								800,000	6,300,000	400,000	3,400,000	1,300,000	[2]	10,200,000	10,200,000	[2]
Loss contingency recognized	1,000,000	1,000,000		1,000,000
Present value abandonment obligation	32,000,000	32,000,000		32,000,000
Number of sites with ownership interest																										40	14
Number of sites with no further action																										10	9
Sites with no further action for soil remediation																										3
Guarantees paid				0
Minimum remaining estimated cost incurred for investigation, remediation and monitoring				20,000,000																						16,000,000	4,000,000
Maximum remaining estimated cost incurred for investigation, remediation and monitoring				45,000,000																						40,000,000	5,000,000
Current and non-current environmental liabilities																									34,000,000	29,000,000	5,000,000
Fossil-fueled EGUs capacity				25
Expected to reduce ozone primary standard level parts per million				0.75
Primary standard for eight hour ozone parts per million						0.07	0.06
Non-regulated operation and maintenance		178,500,000	40,400,000	356,400,000	111,700,000																							20,000,000
Loss contingency accrual, carrying value, payments	$ 7,000,000

[1] Refer to Note 1(b) for discussion of $34 million of charges recognized by Alliant Energy and IPL in the third quarter of 2011 for IPL's forward contracts to purchase SO2 emission allowances.

[2] Alliant Energy reached an agreement with the IRS, which resulted in a favorable determination letter for the Alliant Energy Cash Balance Pension Plan (Plan) during the first quarter of 2011. The agreement with the IRS required Alliant Energy to amend the Plan, which was completed in the second quarter of 2011 resulting in aggregate additional benefits of $10.2 million to be paid to certain former participants in the Plan in the second half of 2011. Alliant Energy recognized $1.3 million and $10.2 million of additional benefits costs during the three and nine months ended Sep. 30, 2011, respectively, related to these benefits. Refer to Note 11(c) for additional information regarding the Plan.