Commitments And Contingencies (Operating Expense Purchase Obligations) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013 MW
Long-term Purchase Commitment [Line Items]
Individual commitments incurred	$ 1
Duane Arnold Energy Center (DAEC) (IPL) [Member] | IPL [Member]
Long-term Purchase Commitment [Line Items]
Approved amount of electric power capacity (in megawatts)	431
Scenario, Forecast [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	2,692
Scenario, Forecast [Member] | IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	2,096
Scenario, Forecast [Member] | WPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	592
Scenario, Forecast [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	19	[1]
Scenario, Forecast [Member] | Other [Member] | IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	9	[1]
Scenario, Forecast [Member] | Other [Member] | WPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	6	[1]
Scenario, Forecast [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	336
Scenario, Forecast [Member] | Natural Gas [Member] | IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	203
Scenario, Forecast [Member] | Natural Gas [Member] | WPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	133
Scenario, Forecast [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	328	[2]
Scenario, Forecast [Member] | Coal [Member] | IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	151	[2]
Scenario, Forecast [Member] | Coal [Member] | WPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	177	[2]
Scenario, Forecast [Member] | SO2 emission allowances [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	34
Scenario, Forecast [Member] | SO2 emission allowances [Member] | IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	34
Scenario, Forecast [Member] | SO2 emission allowances [Member] | WPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0
Scenario, Forecast [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1,975	[3]
Scenario, Forecast [Member] | Purchased Power [Member] | IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1,699	[3]
Scenario, Forecast [Member] | Purchased Power [Member] | WPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	276	[3]
Scenario, Forecast [Member] | Purchased Power [Member] | Duane Arnold Energy Center (DAEC) (IPL) [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1,698	[3],[4]
Scenario, Forecast [Member] | Purchased Power [Member] | Duane Arnold Energy Center (DAEC) (IPL) [Member] | IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1,698	[3],[4]
Scenario, Forecast [Member] | Purchased Power [Member] | Duane Arnold Energy Center (DAEC) (IPL) [Member] | WPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[3],[4]
Scenario, Forecast [Member] | Purchased Power [Member] | Kewaunee Nuclear Power Plant (Kewaunee) (WPL) [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	18	[3]
Scenario, Forecast [Member] | Purchased Power [Member] | Kewaunee Nuclear Power Plant (Kewaunee) (WPL) [Member] | IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[3]
Scenario, Forecast [Member] | Purchased Power [Member] | Kewaunee Nuclear Power Plant (Kewaunee) (WPL) [Member] | WPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	18	[3]
Scenario, Forecast [Member] | Purchased Power [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	259	[3],[5]
Scenario, Forecast [Member] | Purchased Power [Member] | Other [Member] | IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1	[3],[5]
Scenario, Forecast [Member] | Purchased Power [Member] | Other [Member] | WPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	$ 258	[3],[5]

[1] Includes individual commitments incurred during the normal course of business that exceeded $1 million at September 30, 2013.

[2] Corporate Services entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of September 30, 2013 regarding expected future usage, which is subject to change.

[3] Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased.

[4] Includes commitments incurred under an existing PPA that expires February 2014 and a new PPA completed in March 2013. The new PPA grants IPL rights to purchase 431 MWs of capacity and the resulting energy from DAEC for a term from the expiration of the existing PPA in February 2014 through December 31, 2025. If energy delivered under the new PPA is less than the targeted energy amount, an adjustment payment will be made to IPL, which will be reflected in IPL’s energy adjustment clause.

[5] In June 2013, WPL entered into a new PPA for a term from January 1, 2014 through December 31, 2018.