Benefit Plans (Estimated Future And Actual Employer Contributions) (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012 Qualified Defined Benefit Pension Plans [Member] Alliant Energy [Member]	Jun. 30, 2012 Qualified Defined Benefit Pension Plans [Member] IPL [Member]	Jun. 30, 2012 Qualified Defined Benefit Pension Plans [Member] WPL [Member]	Jun. 30, 2012 Non-qualified defined benefit pension plans [Member] Alliant Energy [Member]		Jun. 30, 2012 Directly assigned defined benefit pension plans [Member] IPL [Member]		Jun. 30, 2012 Directly assigned defined benefit pension plans [Member] WPL [Member]		Jun. 30, 2012 Other postretirement benefits plans [Member] Alliant Energy [Member]	Jun. 30, 2012 Other postretirement benefits plans [Member] IPL [Member]	Jun. 30, 2012 Other postretirement benefits plans [Member] WPL [Member]	Dec. 31, 2012 Scenario, Forecast [Member] Qualified Defined Benefit Pension Plans [Member] Alliant Energy [Member]	Dec. 31, 2012 Scenario, Forecast [Member] Qualified Defined Benefit Pension Plans [Member] IPL [Member]	Dec. 31, 2012 Scenario, Forecast [Member] Qualified Defined Benefit Pension Plans [Member] WPL [Member]	Dec. 31, 2012 Scenario, Forecast [Member] Non-qualified defined benefit pension plans [Member] Alliant Energy [Member]		Dec. 31, 2012 Scenario, Forecast [Member] Directly assigned defined benefit pension plans [Member] IPL [Member]		Dec. 31, 2012 Scenario, Forecast [Member] Directly assigned defined benefit pension plans [Member] WPL [Member]		Dec. 31, 2012 Scenario, Forecast [Member] Other postretirement benefits plans [Member] Alliant Energy [Member]	Dec. 31, 2012 Scenario, Forecast [Member] Other postretirement benefits plans [Member] IPL [Member]	Dec. 31, 2012 Scenario, Forecast [Member] Other postretirement benefits plans [Member] WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated for Calendar Year 2012													$ 0	$ 0	$ 0	$ 17.0	[1]	$ 0.8	[2]	$ 0.2	[2]	$ 6.5	$ 2.2	$ 3.9
Actual Through June 30, 2012	$ 0	$ 0	$ 0	$ 2.6	[1]	$ 0.4	[2]	$ 0.1	[2]	$ 3.7	$ 1.5	$ 2.0

[1] Alliant Energy sponsors several non-qualified defined benefit pension plans that cover certain current and former key employees of IPL and WPL. Alliant Energy allocates pension costs to IPL and WPL for these plans.

[2] Amounts directly assigned to IPL and WPL for non-bargaining employees who are participants in Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans.