v2.4.0.6

Summary Of Significant Accounting Policies (Narrative) (Details) (USD $) | 12 Months Ended |  |  | 12 Months Ended |  |  |  |  |  |  | 12 Months Ended |  |  |  |  | 12 Months Ended |  | 12 Months Ended |  |  | 8 Months Ended |  | 12 Months Ended |  | 12 Months Ended |  |  | 12 Months Ended |  |  |  | 12 Months Ended |  |  | 12 Months Ended |  |  |  |  |  |  |  |  | 12 Months Ended |  | 12 Months Ended | 3 Months Ended |  | 12 Months Ended | 1 Months Ended | 12 Months Ended
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Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010 | Dec. 31, 2009 MW | Dec. 31, 2012 Corporate Headquarters [Member] | Dec. 31, 2012 IPL's Tax Benefit Rider [Member] | Dec. 31, 2011 IPL's Tax Benefit Rider [Member] | Dec. 31, 2013 IPL's Tax Benefit Rider [Member] Subsequent Event [Member] Scenario, Forecast [Member] | Dec. 31, 2012 IPL Electric Transmission Assets Sale [Member] | Dec. 31, 2011 IPL Electric Transmission Assets Sale [Member] | Dec. 31, 2012 IPL's Duane Arnold Energy Center (DAEC) Sale [Member] | Dec. 31, 2011 IPL's Duane Arnold Energy Center (DAEC) Sale [Member] | Dec. 31, 2012 IPL's Electric Transmission Service Costs [Member] | Dec. 31, 2011 IPL's Electric Transmission Service Costs [Member] | Dec. 31, 2012 SO2 Emission Allowances [Member] | Dec. 31, 2012 Sheboygan Falls Energy Facility [Member] MW | Dec. 31, 2012 Franklin County Wind Project [Member] MW | Dec. 31, 2012 Vestas Wind Turbine Generators [Member] MW | Dec. 31, 2012 IPL [Member] customer | Dec. 31, 2011 IPL [Member] | Dec. 31, 2010 IPL [Member] | Dec. 31, 2011 IPL [Member] Franklin County Wind Project [Member] | Dec. 31, 2012 IPL [Member] Ottumwa Unit 1 [Member] | Dec. 31, 2012 IPL [Member] George Neal Unit 3 [Member] | Dec. 31, 2012 IPL [Member] George Neal Unit 4 [Member] | Dec. 31, 2012 IPL [Member] IPL's Tax Benefit Rider [Member] | Dec. 31, 2011 IPL [Member] IPL's Tax Benefit Rider [Member] | Dec. 31, 2012 IPL [Member] IPL Electric Transmission Assets Sale [Member] | Dec. 31, 2011 IPL [Member] IPL Electric Transmission Assets Sale [Member] | Dec. 31, 2012 IPL [Member] IPL's Duane Arnold Energy Center (DAEC) Sale [Member] | Dec. 31, 2009 IPL [Member] IPL's Duane Arnold Energy Center (DAEC) Sale [Member] | Dec. 31, 2011 IPL [Member] IPL's Duane Arnold Energy Center (DAEC) Sale [Member] | Dec. 31, 2012 IPL [Member] Iowa [Member] IPL Electric Transmission Assets Sale [Member] | Dec. 31, 2012 IPL [Member] IPL's Electric Transmission Service Costs [Member] | Dec. 31, 2010 IPL [Member] IPL's Electric Transmission Service Costs [Member] | Dec. 31, 2011 IPL [Member] IPL's Electric Transmission Service Costs [Member] | Dec. 31, 2010 IPL [Member] IPL's Electric Transmission Service Costs [Member] Iowa [Member] | Feb. 28, 2010 IPL [Member] IPL Electric Transmission Assets Sale [Member] | Dec. 31, 2007 IPL [Member] IPL Electric Transmission Assets Sale [Member] | Dec. 31, 2012 IPL [Member] IPL Electric Transmission Assets Sale [Member] Iowa [Member] | Dec. 31, 2012 IPL [Member] Sutherland Four Cancellation Costs [Member] | Dec. 31, 2012 IPL [Member] Sutherland Four [Member] IPL's Duane Arnold Energy Center (DAEC) Sale [Member] | Dec. 31, 2010 IPL [Member] Sutherland Four [Member] IPL's Duane Arnold Energy Center (DAEC) Sale [Member] | Dec. 31, 2012 IPL [Member] Franklin County Iowa Wind Site [Member] MW | Dec. 31, 2007 IPL [Member] Franklin County Iowa Wind Site [Member] MW | Dec. 31, 2012 IPL [Member] SO2 Emission Allowances [Member] | Dec. 31, 2007 IPL [Member] SO2 Emission Allowances [Member] | Dec. 31, 2010 IPL [Member] Ipl S Sixth Street Costs [Member] | Dec. 31, 2012 IPL [Member] Franklin County Wind Project [Member] MW | Dec. 31, 2011 IPL [Member] Franklin County Wind Project [Member] MW | Dec. 31, 2010 IPL [Member] Sutherland Four Cancellation Costs [Member] | Dec. 31, 2009 IPL [Member] Sutherland Four [Member] MW | Dec. 31, 2012 IPL [Member] IPL Electric Transmission Assets Sale [Member] | Dec. 31, 2010 IPL [Member] IPL Electric Transmission Assets Sale [Member] Iowa [Member] | Dec. 31, 2012 IPL [Member] Whispering Willow - East Wind Project [Member] | Dec. 31, 2009 IPL [Member] Whispering Willow - East Wind Project [Member] | Dec. 31, 2008 IPL [Member] Whispering Willow - East Wind Project [Member] IUB Cost Cap [Member] MW | Dec. 31, 2011 IPL [Member] Whispering Willow - East Wind Project [Member] Iowa [Member] | Dec. 31, 2012 IPL [Member] Whispering Willow - East Wind Project [Member] Minnesota [Member] | Dec. 31, 2011 IPL [Member] Whispering Willow - East Wind Project [Member] Retail Electric Rate [Member] IPL Electric Transmission Assets Sale [Member] | Dec. 31, 2006 IPL [Member] IPL's Duane Arnold Energy Center (DAEC) Sale [Member] | Dec. 31, 2009 IPL [Member] IPL's Whispering Willow-East Wind Project [Member] MW | Dec. 31, 2009 IPL [Member] IPL's Whispering Willow-East Wind Project [Member] IPL's Duane Arnold Energy Center (DAEC) Sale [Member] | Dec. 31, 2012 IPL [Member] George Neal Unit 3 [Member] | Dec. 31, 2012 IPL [Member] George Neal Unit 4 [Member] | Dec. 31, 2012 IPL [Member] Generation [Member] | Dec. 31, 2011 IPL [Member] Generation [Member] | Dec. 31, 2010 IPL [Member] Generation [Member] | Dec. 31, 2012 IPL [Member] Distribution [Member] | Dec. 31, 2011 IPL [Member] Distribution [Member] | Dec. 31, 2010 IPL [Member] Distribution [Member] | Dec. 31, 2012 IPL [Member] Gas [Member] | Dec. 31, 2011 IPL [Member] Gas [Member] | Dec. 31, 2010 IPL [Member] Gas [Member] | Dec. 31, 2012 WPL [Member] | Dec. 31, 2011 WPL [Member] | Dec. 31, 2010 WPL [Member] | Dec. 31, 2012 WPL [Member] Columbia Units 1-2 [Member] | Dec. 31, 2012 WPL [Member] IPL's Tax Benefit Rider [Member] | Dec. 31, 2011 WPL [Member] IPL's Tax Benefit Rider [Member] | Dec. 31, 2012 WPL [Member] IPL Electric Transmission Assets Sale [Member] | Dec. 31, 2011 WPL [Member] IPL Electric Transmission Assets Sale [Member] | Dec. 31, 2012 WPL [Member] IPL's Duane Arnold Energy Center (DAEC) Sale [Member] | Dec. 31, 2011 WPL [Member] IPL's Duane Arnold Energy Center (DAEC) Sale [Member] | Dec. 31, 2012 WPL [Member] IPL's Electric Transmission Service Costs [Member] | Dec. 31, 2011 WPL [Member] IPL's Electric Transmission Service Costs [Member] | Dec. 31, 2008 WPL [Member] Nelson Dewey Three [Member] MW | Dec. 31, 2012 WPL [Member] Edgewater Unit 5 and Columbia Units 1 and 2 [Member] | Dec. 31, 2011 WPL [Member] Edgewater Unit 5 and Columbia Units 1 and 2 [Member] | Dec. 31, 2011 WPL [Member] Bent Tree - Phase I Wind Project [Member] | Dec. 31, 2010 WPL [Member] Bent Tree - Phase I Wind Project [Member] | Dec. 31, 2012 WPL [Member] Nelson Dewey Three Cancellation Costs [Member] | Dec. 31, 2012 WPL [Member] WPL's Edgewater Unit 5 Purchase [Member] | Dec. 31, 2012 WPL [Member] Riverside Energy Center [Member] MW | Dec. 31, 2012 WPL [Member] Riverside PPA [Member] MW | Jun. 30, 2011 WPL [Member] Green Lake and Fond du Lac Counties Wind Site [Member] | Dec. 31, 2012 WPL [Member] Columbia Units 1-2 [Member] | Dec. 31, 2012 WPL [Member] Generation [Member] | Dec. 31, 2011 WPL [Member] Generation [Member] | Dec. 31, 2010 WPL [Member] Generation [Member] | Dec. 31, 2012 WPL [Member] Generation [Member] Scenario, Forecast [Member] | Dec. 31, 2012 WPL [Member] Distribution [Member] | Dec. 31, 2011 WPL [Member] Distribution [Member] | Dec. 31, 2010 WPL [Member] Distribution [Member] | Dec. 31, 2012 WPL [Member] Distribution [Member] Scenario, Forecast [Member] | Dec. 31, 2012 WPL [Member] Gas [Member] | Dec. 31, 2011 WPL [Member] Gas [Member] | Dec. 31, 2010 WPL [Member] Gas [Member] | Dec. 31, 2012 WPL [Member] Gas [Member] Scenario, Forecast [Member] | Dec. 31, 2012 Alliant Energy And IPL [Member] Ottumwa Unit 1 [Member] | Dec. 31, 2012 Alliant Energy And IPL [Member] IPL's Tax Benefit Rider [Member] | Dec. 31, 2011 Alliant Energy And IPL [Member] IPL's Tax Benefit Rider [Member] | Dec. 31, 2012 Alliant Energy And IPL [Member] IPL's Tax Benefit Rider Decrease In Taxable Income [Member] | Dec. 31, 2011 Alliant Energy And IPL [Member] IPL's Tax Benefit Rider Decrease In Taxable Income [Member] | Dec. 31, 2011 Alliant Energy And IPL [Member] IPL Electric Transmission Assets Sale [Member] 2009 Test Year Retail Electric Request IA Final Order [Member] | Dec. 31, 2011 Alliant Energy And IPL [Member] IPL Electric Transmission Assets Sale [Member] 2009 Test Year Retail Electric Request MN [Member] | Dec. 31, 2010 Alliant Energy And IPL [Member] IPL' s Flood-Related Costs [Member] | Dec. 31, 2010 Alliant Energy And IPL [Member] Ipl S Sixth Street Costs [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] | Dec. 31, 2011 Alliant Energy And IPL [Member] Cross State Air Pollution Rule [Member] Other Long-Term Liabilities And Deferred Credits [Member] | Nov. 30, 2011 Alliant Energy And IPL [Member] Sutherland Four [Member] | Dec. 31, 2011 Alliant Energy And IPL [Member] Sutherland Four [Member] | Dec. 31, 2011 Alliant Energy And IPL [Member] Whispering Willow - East Wind Project [Member] | Dec. 31, 2012 Alliant Energy And IPL [Member] George Neal Units 3 And 4 [Member] | Dec. 31, 2009 Alliant Energy and WPL [Member] Nelson Dewey Three Cancellation Costs [Member] | Dec. 31, 2012 Alliant Energy and WPL [Member] WPL 2013/2014 Test Period Retail Electric And Gas Final Order [Member] | Dec. 31, 2012 Alliant Energy and WPL [Member] Edgewater Unit 5 Emission Controls [Member] | Dec. 31, 2012 Alliant Energy and WPL [Member] Columbia Units 1-2 [Member] | Dec. 31, 2012 IPL and WPL [Member] Whispering Willow - East Wind Project [Member] Bent Tree - Phase I Wind Project [Member] MW | Dec. 31, 2012 Franklin County Wind Project [Member] | Dec. 31, 2012 Sheboygan Falls Energy Facility [Member] | Dec. 31, 2012 Non-Regulated [Member] Minimum [Member] | Dec. 31, 2012 Non-Regulated [Member] Maximum [Member] | Dec. 31, 2013 Electric [Member] IPL's Tax Benefit Rider [Member] Scenario, Forecast [Member] | Dec. 31, 2013 Gas [Member] IPL's Tax Benefit Rider [Member] Scenario, Forecast [Member]
General: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Generation and distribution of steam, number of customers served (in customers) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fossil-fueled EGUs capacity (in megawatts) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 300 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 630 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 300 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Captial lease, lease term | 20 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Capacity of electricity generation unit (in megawatts) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 100 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Assets and Regulatory Liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory assets representing past expenditures that did not earn a return |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 68,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 13,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Simple average of actual costs incurred during test year, simple average basis |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Expenditure collection period after new rate implementation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term purchase commitment, amount | 982,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  | 34,000,000 | [1] |  |  |  | 537,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 34,000,000 | [1] | 34,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 303,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 34,000,000 | 34,000,000 | 34,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase (decrease) in regulatory assets and liabilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 30,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory assets | 1,612,400,000 | 1,495,000,000 |  |  |  |  |  |  |  |  |  |  | 16,600,000 | 24,900,000 |  |  |  |  |  | 1,217,900,000 | 1,117,300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  | 16,600,000 |  | 24,900,000 | 41,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 394,500,000 | 377,700,000 |  |  |  |  |  |  |  |  | 0 | 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 7,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amounts not probable of recovery |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 4,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Electric production fuel and energy purchases | 712,300,000 | 764,500,000 | 819,200,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 344,500,000 | 383,100,000 | 418,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 367,800,000 | 381,400,000 | 401,200,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Utility - other operation and maintenance | 590,000,000 | 630,200,000 | 617,200,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 350,000,000 | 375,000,000 | 384,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 240,000,000 | 255,200,000 | 232,700,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5,000,000 | 7,000,000 | 2,000,000 |  | 2,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amortization of regulatory asset |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 8,000,000 |  |  |  |  |  |  | 5,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liabilities | 916,100,000 | 910,100,000 |  |  |  | 355,800,000 | 349,600,000 |  | 32,500,000 | 45,100,000 | 9,500,000 | 14,600,000 |  |  |  |  |  |  |  | 701,400,000 | 721,300,000 |  |  |  |  |  | 355,800,000 | 349,600,000 | 32,500,000 | 45,100,000 | 9,500,000 |  | 14,600,000 |  | 41,000,000 |  |  |  |  | 89,000,000 |  |  |  | 26,000,000 |  |  |  |  |  |  |  |  |  |  | 46,000,000 | 46,000,000 |  |  |  | 23,000,000 |  | 3,000,000 |  |  | 29,000,000 |  |  |  |  |  |  |  |  |  |  |  | 214,700,000 | 188,800,000 |  |  | 0 | 0 | 0 | 0 | 0 | 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fossil-fueled EGUs capacity (in megawatts) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 300 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 630 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 300 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Recovery of direct costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 26,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,000,000 |  |  |  | 11,000,000 |  |  |  |  |  |  |  |  |  |
Recovery of dIrect costs, recovery period |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 25 years |  |  |  | 5 years |  |  |  |  |  |  |  |  |  |
Amortization period of regulatory assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5 years | 5 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase in regulatory assets | 178,100,000 | 413,100,000 | 20,800,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 129,000,000 | 328,800,000 | 49,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 49,100,000 | 84,300,000 | (28,700,000) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 16,000,000 |  |  |  |  | 2,000,000 |  |  |  | 5,000,000 |  |  |  |  |  |  |  |  |
Credit to utility other operation and maintenance |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,000,000 |  |  |  | 5,000,000 |  |  |  |  |  |  |  |  |
Recognized impairment charges, regulatory assets |  | 9,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 7,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Jointly owned utility plant, proportionate ownership share |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 48.00% | 28.00% | 25.70% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 70.00% |  |  | 28.00% | 25.695% |  |  |  |  |  |  |  |  |  |  |  |  | 46.20% |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 25.00% |  |  |  | 46.20% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Allowance for funds used during construction | 21,900,000 | 12,000,000 | 18,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 8,400,000 | 5,800,000 | 5,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 14,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 13,500,000 | 6,200,000 | 12,500,000 |  |  |  |  |  |  |  |  |  |  | 11,000,000 | 3,000,000 | 1,000,000 | 10,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,000,000 |  |  | 11,000,000 | 4,000,000 |  |  |  |  |  |  |
Increase (decrease) in regulatory liabilities | 16,400,000 | 168,300,000 | 8,400,000 |  |  |  |  | (24,000,000) |  |  |  |  |  |  |  |  |  |  |  | (12,100,000) | 156,300,000 | 17,500,000 |  |  |  |  |  |  |  |  | (5,000,000) | 12,000,000 |  | (8,000,000) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 59,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  | 28,500,000 | 12,000,000 | (9,100,000) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (83,000,000) | (61,000,000) |  |  | 19,000,000 | 5,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (56,000,000) | (12,000,000)
Income tax expense (benefit) | 89,400,000 | 69,200,000 | 147,700,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (19,800,000) | (3,600,000) | 42,300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 94,600,000 | 81,900,000 | 98,300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (48,000,000) | (36,000,000) | (35,000,000) | (25,000,000) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reduction in electric customer rates |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 12,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amortization period of regulatory liabilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5 years |  | 5 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Utility Property, Plant and Equipment: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Electric capacity of wind project (in megawatts) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 100 | 500 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 200 | 500 |  |  |  |  | 100 | 100 |  |  |  |  |  |  | 200 |  |  |  |  | 200 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 400 |  |  |  |  |  |
Capitalized costs recorded in Other property, plant and equipment | 403,500,000 | 0 | 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 13,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  | 417,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 403,500,000 | 0 | 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 403,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 72,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 66,000,000 |  |  | 132,000,000 | 126,000,000 |  |  |  |  |  |  |
Amount of electrical capacity (in megawatts) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 600 | 490 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Asset impairment loss |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 21,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 8,000,000 |  |  |  |  |  |  |  |  |  |  |  |
Disallowed recovery of project costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 8,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Project costs allocated by jurisdiction |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 30,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from sale of wind project assets to affiliate |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0 | 115,300,000 | 0 | 115,300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Purchase of development rights (in megawatts) |  |  |  | 100 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Jointly owned utility plant, proportionate ownership share |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 48.00% | 28.00% | 25.70% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 70.00% |  |  | 28.00% | 25.695% |  |  |  |  |  |  |  |  |  |  |  |  | 46.20% |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 25.00% |  |  |  | 46.20% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Allowance for funds used during construction | 21,900,000 | 12,000,000 | 18,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 8,400,000 | 5,800,000 | 5,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 14,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 13,500,000 | 6,200,000 | 12,500,000 |  |  |  |  |  |  |  |  |  |  | 11,000,000 | 3,000,000 | 1,000,000 | 10,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,000,000 |  |  | 11,000,000 | 4,000,000 |  |  |  |  |  |  |
Intangible assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 8,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Intangible asset amortization expense, 2013 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5,400,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Intangible asset amortization expense, 2014 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,600,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Average rate of depreciation for public utilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3.70% | 3.50% | 3.70% | 2.50% | 2.40% | 2.70% | 3.40% | 3.50% | 3.30% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3.20% | 3.30% | 2.90% | 3.40% | 2.90% | 2.90% | 2.60% | 2.70% | 2.60% | 2.60% | 2.20% | 2.50% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Non-regulated and Other Property, Plant and Equipment: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated useful life |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 30 years | 35 years | 5 years | 30 years |  |
Non-regulated generation property plant and equipment | 258,600,000 | 270,600,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 148,000,000 | 111,000,000 |  |  |  |
Capitalized expenditures |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 130,000,000 |  |  |  |  |
Capitalized interest |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 9,000,000 |  |  |  |  |
Asset retirement obligation | 101,500,000 | 91,100,000 | 75,900,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 45,500,000 | 56,200,000 | 43,600,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 46,900,000 | 34,900,000 | 32,300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 9,000,000 |  |  |  |  |
Increase in Alliant Energy Corporate Services, Inc. and other property, plant and equipment | 132,600,000 | 65,300,000 | 33,600,000 |  | 48,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Operating Revenues: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated recovery of overaccrued operating revenue, reflected on customer billing, maximum period |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Final settlement recovery of overaccrued operating revenue, reflected on customer billing, maximum period |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Utility Cost Recovery Mechanisms: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Contingent agreement, electric base rate case not to be filed, period |  |  | 3 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Other Comprehensive Income: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Other comprehensive income | $ 0 | $ 600,000 | $ 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
[1] | 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.

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- Definition Fossil Fueled Energy Generating Units Capacity + References No definition available. + Details
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Data Type: | num:powerItemType
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Period Type: | duration

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- Details
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- Definition Generation and Distribution of Steam, Number of Customers Served + References No definition available. + Details
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- Details
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- Definition The cash outflow for purchases of and capital improvements on property, plant and equipment (capital expenditures), software, and other intangible assets for the utility business. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition The cash outflow for purchases of and capital improvements on property, plant and equipment (capital expenditures), software, and other intangible assets for Alliant Energy Corporate Services, Inc. and non-regulated business. + References No definition available. + Details
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- Definition Public Utilities, Property, Plant and Equipment, Amount of Electrical Capacity + References No definition available. + Details
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- Definition The sum of capitalized costs relating to oil and gas producing activities before accounting for accumulated depreciation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e61901-109447 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 19 -Paragraph 59M -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
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- Details
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- Definition Discloses the amount of operating expense for the period for routine plant maintenance, repairs and operations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.2(b)) -URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688 + Details
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