Commitments And Contingencies (Narrative) (Details) - Jun. 30, 2015 $ in Millions	USD ($) site
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 2,277
Performance guarantees outstanding	198
Present value abandonment obligation	36
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 1,799
Number of sites monitoring and remediating (in sites) | site	24
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 478
Number of sites monitoring and remediating (in sites) | site	5
Capital Purchase Obligation [Member] | Alliant Energy and WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 30
Performance guarantees outstanding, 2015 [Member]
Commitments and Contingencies [Line Items]
Performance guarantees outstanding	75
Performance guarantees outstanding, 2016 [Member]
Commitments and Contingencies [Line Items]
Performance guarantees outstanding	48
Performance guarantees outstanding, 2017 [Member]
Commitments and Contingencies [Line Items]
Performance guarantees outstanding	75
Civil Penalty [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Environmental mitigation projects to be completed, value	1
Environmental Issue [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Environmental mitigation projects to be completed, value	6
Environmental Issue [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Environmental mitigation projects to be completed, value	$ 7
Minimum [Member]
Commitments and Contingencies [Line Items]
Warranty period	12 months
Maximum [Member]
Commitments and Contingencies [Line Items]
Warranty period	60 months