Commitments And Contingencies (Operating Expense Purchase Obligations) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012
Long-term Purchase Commitment [Line Items]
Individual commitments incurred	$ 1
Scenario, Forecast [Member] | Alliant Energy Corporation [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1,140
Scenario, Forecast [Member] | IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	634
Scenario, Forecast [Member] | WPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	381
Scenario, Forecast [Member] | Other [Member] | Alliant Energy Corporation [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	41
Scenario, Forecast [Member] | Other [Member] | IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	19
Scenario, Forecast [Member] | Other [Member] | WPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	22
Scenario, Forecast [Member] | Natural Gas [Member] | Alliant Energy Corporation [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	255
Scenario, Forecast [Member] | Natural Gas [Member] | IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	120
Scenario, Forecast [Member] | Natural Gas [Member] | WPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	135
Scenario, Forecast [Member] | Coal [Member] | Alliant Energy Corporation [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	274
Scenario, Forecast [Member] | Coal [Member] | IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	88
Scenario, Forecast [Member] | Coal [Member] | WPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	61
Scenario, Forecast [Member] | Coal [Member] | Corporate Services [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	125
Scenario, Forecast [Member] | Sulfur Dioxide (SO2) Emission Allowances [Member] | Alliant Energy Corporation [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	34
Scenario, Forecast [Member] | Sulfur Dioxide (SO2) Emission Allowances [Member] | IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	34
Scenario, Forecast [Member] | Purchased Power [Member] | Alliant Energy Corporation [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	536
Scenario, Forecast [Member] | Purchased Power [Member] | IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	373
Scenario, Forecast [Member] | Purchased Power [Member] | WPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	163
Scenario, Forecast [Member] | Purchased Power [Member] | Duane Arnold Energy Center (DAEC) (IPL) [Member] | Alliant Energy Corporation [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	364
Scenario, Forecast [Member] | Purchased Power [Member] | Duane Arnold Energy Center (DAEC) (IPL) [Member] | IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	364
Scenario, Forecast [Member] | Purchased Power [Member] | Kewaunee WPL [Member] | Alliant Energy Corporation [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	131
Scenario, Forecast [Member] | Purchased Power [Member] | Kewaunee WPL [Member] | WPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	131
Scenario, Forecast [Member] | Purchased Power [Member] | Other [Member] | Alliant Energy Corporation [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	41
Scenario, Forecast [Member] | Purchased Power [Member] | Other [Member] | IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	9
Scenario, Forecast [Member] | Purchased Power [Member] | Other [Member] | WPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	$ 32