v2.4.0.6
Commitments And Contingencies (Operating Expense Purchase Obligations) (Details) (USD $)
 12 Months Ended 1 Months Ended 12 Months Ended
Dec. 31, 2012
Dec. 31, 2012
Purchased Power [Member]
Dec. 31, 2012
DAEC IPL [Member]
Dec. 31, 2012
Kewaunee WPL [Member]
Dec. 31, 2012
Other [Member]
Dec. 31, 2012
Natural Gas [Member]
Dec. 31, 2012
Coal [Member]
Dec. 31, 2012
SO2 emission allowances [Member]
Dec. 31, 2012
Other [Member]
Dec. 31, 2012
2013 [Member]
Dec. 31, 2012
2013 [Member]
Purchased Power [Member]
Dec. 31, 2012
2013 [Member]
DAEC IPL [Member]
Dec. 31, 2012
2013 [Member]
Kewaunee WPL [Member]
Dec. 31, 2012
2013 [Member]
Other [Member]
Dec. 31, 2012
2013 [Member]
Natural Gas [Member]
Dec. 31, 2012
2013 [Member]
Coal [Member]
Dec. 31, 2012
2013 [Member]
SO2 emission allowances [Member]
Dec. 31, 2012
2013 [Member]
Other [Member]
Dec. 31, 2012
2014 [Member]
Dec. 31, 2012
2014 [Member]
Purchased Power [Member]
Dec. 31, 2012
2014 [Member]
DAEC IPL [Member]
Dec. 31, 2012
2014 [Member]
Kewaunee WPL [Member]
Dec. 31, 2012
2014 [Member]
Other [Member]
Dec. 31, 2012
2014 [Member]
Natural Gas [Member]
Dec. 31, 2012
2014 [Member]
Coal [Member]
Dec. 31, 2012
2014 [Member]
SO2 emission allowances [Member]
Dec. 31, 2012
2014 [Member]
Other [Member]
Dec. 31, 2012
2015 [Member]
Dec. 31, 2012
2015 [Member]
Purchased Power [Member]
Dec. 31, 2012
2015 [Member]
DAEC IPL [Member]
Dec. 31, 2012
2015 [Member]
Kewaunee WPL [Member]
Dec. 31, 2012
2015 [Member]
Other [Member]
Dec. 31, 2012
2015 [Member]
Natural Gas [Member]
Dec. 31, 2012
2015 [Member]
Coal [Member]
Dec. 31, 2012
2015 [Member]
SO2 emission allowances [Member]
Dec. 31, 2012
2015 [Member]
Other [Member]
Dec. 31, 2012
2016 [Member]
Dec. 31, 2012
2016 [Member]
Purchased Power [Member]
Dec. 31, 2012
2016 [Member]
DAEC IPL [Member]
Dec. 31, 2012
2016 [Member]
Kewaunee WPL [Member]
Dec. 31, 2012
2016 [Member]
Other [Member]
Dec. 31, 2012
2016 [Member]
Natural Gas [Member]
Dec. 31, 2012
2016 [Member]
Coal [Member]
Dec. 31, 2012
2016 [Member]
SO2 emission allowances [Member]
Dec. 31, 2012
2016 [Member]
Other [Member]
Dec. 31, 2012
2017 [Member]
Dec. 31, 2012
2017 [Member]
Purchased Power [Member]
Dec. 31, 2012
2017 [Member]
DAEC IPL [Member]
Dec. 31, 2012
2017 [Member]
Kewaunee WPL [Member]
Dec. 31, 2012
2017 [Member]
Other [Member]
Dec. 31, 2012
2017 [Member]
Natural Gas [Member]
Dec. 31, 2012
2017 [Member]
Coal [Member]
Dec. 31, 2012
2017 [Member]
SO2 emission allowances [Member]
Dec. 31, 2012
2017 [Member]
Other [Member]
Dec. 31, 2012
Thereafter [Member]
Dec. 31, 2012
Thereafter [Member]
Purchased Power [Member]
Dec. 31, 2012
Thereafter [Member]
DAEC IPL [Member]
Dec. 31, 2012
Thereafter [Member]
Kewaunee WPL [Member]
Dec. 31, 2012
Thereafter [Member]
Other [Member]
Dec. 31, 2012
Thereafter [Member]
Natural Gas [Member]
Dec. 31, 2012
Thereafter [Member]
Coal [Member]
Dec. 31, 2012
Thereafter [Member]
SO2 emission allowances [Member]
Dec. 31, 2012
Thereafter [Member]
Other [Member]
Dec. 31, 2012
IPL [Member]
Dec. 31, 2012
IPL [Member]
Purchased Power [Member]
Jan. 31, 2013
IPL [Member]
DAEC IPL [Member]
Subsequent Event [Member]
MW
Dec. 31, 2012
IPL [Member]
DAEC [Member]
Dec. 31, 2012
IPL [Member]
Other [Member]
Dec. 31, 2012
IPL [Member]
Natural Gas [Member]
Dec. 31, 2012
IPL [Member]
Coal [Member]
Dec. 31, 2012
IPL [Member]
SO2 emission allowances [Member]
Dec. 31, 2007
IPL [Member]
SO2 emission allowances [Member]
Dec. 31, 2012
IPL [Member]
Other [Member]
Dec. 31, 2012
IPL [Member]
2013 [Member]
Dec. 31, 2012
IPL [Member]
2013 [Member]
Purchased Power [Member]
Dec. 31, 2012
IPL [Member]
2013 [Member]
DAEC [Member]
Dec. 31, 2012
IPL [Member]
2013 [Member]
Other [Member]
Dec. 31, 2012
IPL [Member]
2013 [Member]
Natural Gas [Member]
Dec. 31, 2012
IPL [Member]
2013 [Member]
Coal [Member]
Dec. 31, 2012
IPL [Member]
2013 [Member]
SO2 emission allowances [Member]
Dec. 31, 2012
IPL [Member]
2013 [Member]
Other [Member]
Dec. 31, 2012
IPL [Member]
2014 [Member]
Dec. 31, 2012
IPL [Member]
2014 [Member]
Purchased Power [Member]
Dec. 31, 2012
IPL [Member]
2014 [Member]
DAEC [Member]
Dec. 31, 2012
IPL [Member]
2014 [Member]
Other [Member]
Dec. 31, 2012
IPL [Member]
2014 [Member]
Natural Gas [Member]
Dec. 31, 2012
IPL [Member]
2014 [Member]
Coal [Member]
Dec. 31, 2012
IPL [Member]
2014 [Member]
SO2 emission allowances [Member]
Dec. 31, 2012
IPL [Member]
2014 [Member]
Other [Member]
Dec. 31, 2012
IPL [Member]
2015 [Member]
Dec. 31, 2012
IPL [Member]
2015 [Member]
Purchased Power [Member]
Dec. 31, 2012
IPL [Member]
2015 [Member]
DAEC [Member]
Dec. 31, 2012
IPL [Member]
2015 [Member]
Other [Member]
Dec. 31, 2012
IPL [Member]
2015 [Member]
Natural Gas [Member]
Dec. 31, 2012
IPL [Member]
2015 [Member]
Coal [Member]
Dec. 31, 2012
IPL [Member]
2015 [Member]
SO2 emission allowances [Member]
Dec. 31, 2012
IPL [Member]
2015 [Member]
Other [Member]
Dec. 31, 2012
IPL [Member]
2016 [Member]
Dec. 31, 2012
IPL [Member]
2016 [Member]
Purchased Power [Member]
Dec. 31, 2012
IPL [Member]
2016 [Member]
DAEC [Member]
Dec. 31, 2012
IPL [Member]
2016 [Member]
Other [Member]
Dec. 31, 2012
IPL [Member]
2016 [Member]
Natural Gas [Member]
Dec. 31, 2012
IPL [Member]
2016 [Member]
Coal [Member]
Dec. 31, 2012
IPL [Member]
2016 [Member]
SO2 emission allowances [Member]
Dec. 31, 2012
IPL [Member]
2016 [Member]
Other [Member]
Dec. 31, 2012
IPL [Member]
2017 [Member]
Dec. 31, 2012
IPL [Member]
2017 [Member]
Purchased Power [Member]
Dec. 31, 2012
IPL [Member]
2017 [Member]
DAEC [Member]
Dec. 31, 2012
IPL [Member]
2017 [Member]
Other [Member]
Dec. 31, 2012
IPL [Member]
2017 [Member]
Natural Gas [Member]
Dec. 31, 2012
IPL [Member]
2017 [Member]
Coal [Member]
Dec. 31, 2012
IPL [Member]
2017 [Member]
SO2 emission allowances [Member]
Dec. 31, 2012
IPL [Member]
2017 [Member]
Other [Member]
Dec. 31, 2012
IPL [Member]
Thereafter [Member]
Dec. 31, 2012
IPL [Member]
Thereafter [Member]
Purchased Power [Member]
Dec. 31, 2012
IPL [Member]
Thereafter [Member]
DAEC [Member]
Dec. 31, 2012
IPL [Member]
Thereafter [Member]
Other [Member]
Dec. 31, 2012
IPL [Member]
Thereafter [Member]
Natural Gas [Member]
Dec. 31, 2012
IPL [Member]
Thereafter [Member]
Coal [Member]
Dec. 31, 2012
IPL [Member]
Thereafter [Member]
SO2 emission allowances [Member]
Dec. 31, 2012
IPL [Member]
Thereafter [Member]
Other [Member]
Dec. 31, 2012
WPL [Member]
Dec. 31, 2012
WPL [Member]
Purchased Power [Member]
Dec. 31, 2012
WPL [Member]
Kewaunee [Member]
Dec. 31, 2012
WPL [Member]
Other [Member]
Dec. 31, 2012
WPL [Member]
Natural Gas [Member]
Dec. 31, 2012
WPL [Member]
Coal [Member]
Dec. 31, 2012
WPL [Member]
Other [Member]
Dec. 31, 2012
WPL [Member]
2013 [Member]
Dec. 31, 2012
WPL [Member]
2013 [Member]
Purchased Power [Member]
Dec. 31, 2012
WPL [Member]
2013 [Member]
Kewaunee [Member]
Dec. 31, 2012
WPL [Member]
2013 [Member]
Other [Member]
Dec. 31, 2012
WPL [Member]
2013 [Member]
Natural Gas [Member]
Dec. 31, 2012
WPL [Member]
2013 [Member]
Coal [Member]
Dec. 31, 2012
WPL [Member]
2013 [Member]
Other [Member]
Dec. 31, 2012
WPL [Member]
2014 [Member]
Dec. 31, 2012
WPL [Member]
2014 [Member]
Purchased Power [Member]
Dec. 31, 2012
WPL [Member]
2014 [Member]
Kewaunee [Member]
Dec. 31, 2012
WPL [Member]
2014 [Member]
Other [Member]
Dec. 31, 2012
WPL [Member]
2014 [Member]
Natural Gas [Member]
Dec. 31, 2012
WPL [Member]
2014 [Member]
Coal [Member]
Dec. 31, 2012
WPL [Member]
2014 [Member]
Other [Member]
Dec. 31, 2012
WPL [Member]
2015 [Member]
Dec. 31, 2012
WPL [Member]
2015 [Member]
Purchased Power [Member]
Dec. 31, 2012
WPL [Member]
2015 [Member]
Kewaunee [Member]
Dec. 31, 2012
WPL [Member]
2015 [Member]
Other [Member]
Dec. 31, 2012
WPL [Member]
2015 [Member]
Natural Gas [Member]
Dec. 31, 2012
WPL [Member]
2015 [Member]
Coal [Member]
Dec. 31, 2012
WPL [Member]
2015 [Member]
Other [Member]
Dec. 31, 2012
WPL [Member]
2016 [Member]
Dec. 31, 2012
WPL [Member]
2016 [Member]
Purchased Power [Member]
Dec. 31, 2012
WPL [Member]
2016 [Member]
Kewaunee [Member]
Dec. 31, 2012
WPL [Member]
2016 [Member]
Other [Member]
Dec. 31, 2012
WPL [Member]
2016 [Member]
Natural Gas [Member]
Dec. 31, 2012
WPL [Member]
2016 [Member]
Coal [Member]
Dec. 31, 2012
WPL [Member]
2016 [Member]
Other [Member]
Dec. 31, 2012
WPL [Member]
2017 [Member]
Dec. 31, 2012
WPL [Member]
2017 [Member]
Purchased Power [Member]
Dec. 31, 2012
WPL [Member]
2017 [Member]
Kewaunee [Member]
Dec. 31, 2012
WPL [Member]
2017 [Member]
Other [Member]
Dec. 31, 2012
WPL [Member]
2017 [Member]
Natural Gas [Member]
Dec. 31, 2012
WPL [Member]
2017 [Member]
Coal [Member]
Dec. 31, 2012
WPL [Member]
2017 [Member]
Other [Member]
Dec. 31, 2012
WPL [Member]
Thereafter [Member]
Dec. 31, 2012
WPL [Member]
Thereafter [Member]
Purchased Power [Member]
Dec. 31, 2012
WPL [Member]
Thereafter [Member]
Kewaunee [Member]
Dec. 31, 2012
WPL [Member]
Thereafter [Member]
Other [Member]
Dec. 31, 2012
WPL [Member]
Thereafter [Member]
Natural Gas [Member]
Dec. 31, 2012
WPL [Member]
Thereafter [Member]
Coal [Member]
Dec. 31, 2012
WPL [Member]
Thereafter [Member]
Other [Member]
Dec. 31, 2012
Corporate Services [Member]
2013 [Member]
Coal [Member]
Scenario, Forecast [Member]
Dec. 31, 2012
Corporate Services [Member]
2014 [Member]
Coal [Member]
Scenario, Forecast [Member]
Dec. 31, 2012
Corporate Services [Member]
2015 [Member]
Coal [Member]
Scenario, Forecast [Member]
Dec. 31, 2012
Corporate Services [Member]
2016 [Member]
Coal [Member]
Scenario, Forecast [Member]
Dec. 31, 2012
Corporate Services [Member]
2017 [Member]
Coal [Member]
Scenario, Forecast [Member]
Dec. 31, 2011
Alliant Energy And IPL [Member]
SO2 emission allowances [Member]
Dec. 31, 2011
Alliant Energy And IPL [Member]
Cross State Air Pollution Rule [Member]
Long-term Purchase Commitment [Line Items]                                                                                                                                                                                                                                                                                                                                                                  
Minimum future commitments $ 982,000,000 $ 363,000,000 [1] $ 234,000,000 [1],[2] $ 77,000,000 [1] $ 52,000,000 [1] $ 292,000,000 $ 264,000,000 [3] $ 34,000,000 [4] $ 29,000,000 [5] $ 596,000,000 $ 285,000,000 [1] $ 200,000,000 [1],[2] $ 77,000,000 [1] $ 8,000,000 [1] $ 163,000,000 $ 126,000,000 [3] $ 0 [4] $ 22,000,000 [5] $ 187,000,000 $ 48,000,000 [1] $ 34,000,000 [1],[2] $ 0 [1] $ 14,000,000 [1] $ 55,000,000 $ 80,000,000 [3] $ 0 [4] $ 4,000,000 [5] $ 126,000,000 $ 30,000,000 [1] $ 0 [1],[2] $ 0 [1] $ 30,000,000 [1] $ 37,000,000 $ 44,000,000 [3] $ 12,000,000 [4] $ 3,000,000 [5] $ 45,000,000 $ 0 [1] $ 0 [1],[2] $ 0 [1] $ 0 [1] $ 21,000,000 $ 10,000,000 [3] $ 14,000,000 [4] $ 0 [5] $ 22,000,000 $ 0 [1] $ 0 [1],[2] $ 0 [1] $ 0 [1] $ 10,000,000 $ 4,000,000 [3] $ 8,000,000 [4] $ 0 [5] $ 6,000,000 $ 0 [1] $ 0 [1],[2] $ 0 [1] $ 0 [1] $ 6,000,000 $ 0 [3] $ 0 [4] $ 0 [5] $ 537,000,000 $ 235,000,000 [1]   $ 234,000,000 [1],[2] $ 1,000,000 [1] $ 176,000,000 $ 80,000,000 [3] $ 34,000,000 [4] $ 34,000,000 $ 12,000,000 [5] $ 355,000,000 $ 201,000,000 [1] $ 200,000,000 [1],[2] $ 1,000,000 [1] $ 109,000,000 $ 36,000,000 [3] $ 0 [4] $ 9,000,000 [5] $ 93,000,000 $ 34,000,000 [1] $ 34,000,000 [1],[2] $ 0 [1] $ 29,000,000 $ 28,000,000 [3] $ 0 [4] $ 2,000,000 [5] $ 45,000,000 $ 0 [1] $ 0 [1],[2] $ 0 [1] $ 21,000,000 $ 11,000,000 [3] $ 12,000,000 [4] $ 1,000,000 [5] $ 27,000,000 $ 0 [1] $ 0 [1],[2] $ 0 [1] $ 8,000,000 $ 5,000,000 [3] $ 14,000,000 [4] $ 0 [5] $ 11,000,000 $ 0 [1] $ 0 [1],[2] $ 0 [1] $ 3,000,000 $ 0 [3] $ 8,000,000 [4] $ 0 [5] $ 6,000,000 $ 0 [1] $ 0.0 [1],[2] $ 0 [1] $ 6,000,000 $ 0 [3] $ 0 [4] $ 0 [5] $ 303,000,000 $ 128,000,000 [1] $ 77,000,000 [1] $ 51,000,000 [1] $ 116,000,000 $ 48,000,000 [3] $ 11,000,000 [5] $ 168,000,000 $ 84,000,000 [1] $ 77,000,000 [1] $ 7,000,000 [1] $ 54,000,000 $ 19,000,000 [3] $ 11,000,000 [5] $ 58,000,000 $ 14,000,000 [1] $ 0 [1] $ 14,000,000 [1] $ 26,000,000 $ 18,000,000 [3] $ 0 [5] $ 57,000,000 $ 30,000,000 [1] $ 0 [1] $ 30,000,000 [1] $ 16,000,000 $ 11,000,000 [3] $ 0 [5] $ 13,000,000 $ 0 [1] $ 0 [1] $ 0 [1] $ 13,000,000 $ 0 [3] $ 0 [5] $ 7,000,000 $ 0 [1] $ 0 [1] $ 0 [1] $ 7,000,000 $ 0 [3] $ 0 [5] $ 0 $ 0 [1] $ 0 [1] $ 0 [1] $ 0 $ 0 [3] $ 0 [5] $ 71,000,000 $ 34,000,000 $ 22,000,000 $ 5,000,000 $ 4,000,000 $ 34,000,000 $ 34,000,000
Approved amount of electric power capacity (in megawatts)                                                                                                                                   431                                                                                                                                                                                                                              
Individual commitments incurred $ 1,000,000                                                                                                                                                                                                                                                                                                                                                                
[1] Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. Refer to Note 19 for additional information on purchased power transactions.
[2] IPL is obligated to pay for capacity and energy delivered under the DAEC PPA. If energy delivered under the DAEC PPA is less than the targeted energy amount, an adjustment payment is made to IPL, which is reflected in IPL’s energy adjustment clause. In January 2013, the IUB issued an order approving a proposed DAEC PPA, with 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. As of December 31, 2012, there was no minimum future commitment for the proposed DAEC PPA.
[3] IPL and WPL entered into coal contracts (directly assigned to certain generating stations) and coal transportation contracts (directly assigned to corresponding transloading terminals), the amounts of which are included in each of the tables above. Also included in Alliant Energy’s and IPL’s tables is IPL’s respective portion of coal and coal transportation contracts related to jointly-owned generating stations not operated by IPL. In addition, Corporate Services entered into system-wide coal contracts on behalf of IPL and WPL of $71 million, $34 million, $22 million, $5 million and $4 million for 2013, 2014, 2015, 2016 and 2017, respectively, to allow flexibility for the changing needs of the quantity of coal consumed by each. Coal contract quantities are allocated to specific IPL or WPL generating stations at or before the time of delivery based on various factors including projected heat input requirements, combustion compatibility and efficiency. These system-wide coal contracts have not been directly assigned to IPL and WPL since the specific needs of each utility were not yet known as of December 31, 2012 and therefore are excluded from IPL’s and WPL’s tables above.
[4] Refer to Note 1(b) for discussion of $34 million of charges recognized by Alliant Energy and IPL in 2011 for forward contracts to purchase SO2 emission allowances.
[5] Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2012.