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.