v2.4.0.6
Condensed Consolidated Balance Sheets (USD $)
In Millions, unless otherwise specified
Sep. 30, 2012
Dec. 31, 2011
Utility:    
Electric plant in service $ 8,335.4 $ 8,165.4
Gas plant in service 869.4 852.9
Other plant in service 512.5 510.1
Accumulated depreciation (3,351.5) (3,206.0)
Net plant 6,365.8 6,322.4
Construction work in progress:    
Edgewater Generating Station Unit 5 emission controls (Wisconsin Power and Light Company) 124.0 77.7
Columbia Energy Center Units 1 and 2 emission controls (Wisconsin Power and Light Company) 91.6 9.0
George Neal Generating Station Units 3 and 4 emission controls (Interstate Power and Light Company) 53.5 8.3
Ottumwa Generating Station Unit 1 emission controls (Interstate Power and Light Company) 53.3 7.7
Other 159.1 154.5
Other, less accumulated depreciation 21.3 34.9
Total utility 6,868.6 6,614.5
Non-regulated and other:    
Non-regulated Generation, less accumulated depreciation 326.5 270.6
Alliant Energy Corporate Services, Inc. and other, less accumulated depreciation 189.5 148.2
Total non-regulated and other 516.0 418.8
Total property, plant and equipment 7,384.6 7,033.3
Current assets:    
Cash and cash equivalents 41.1 11.4
Accounts receivable:    
Customer, less allowance for doubtful accounts 93.9 88.1
Unbilled utility revenues 59.8 75.1
Other, less allowance for doubtful accounts 239.7 114.9
Income tax refunds receivable 43.9 39.1
Production fuel, at weighted average cost 110.5 101.9
Materials and supplies, at weighted average cost 61.4 58.5
Gas stored underground, at weighted average cost 37.3 57.7
Regulatory assets 92.9 103.6
Derivative assets 35.9 12.7
Prepaid gross receipts tax 29.1 40.2
Deferred income tax assets 90.0 22.8
Assets held for sale 51.4 119.6
Prepayments and other 41.7 25.0
Total current assets 1,028.6 870.6
Investments:    
Investment in American Transmission Company LLC 253.2 238.8
Other 60.9 61.9
Total investments 314.1 300.7
Other assets:    
Regulatory assets 1,425.5 1,391.4
Deferred charges and other 98.1 91.9
Total other assets 1,523.6 1,483.3
Total assets 10,250.9 9,687.9
Stockholders' Equity Attributable to Parent [Abstract]    
Common stock 1.1 1.1
Additional paid-in capital 1,512.1 1,510.8
Retained earnings 1,612.1 1,510.2
Accumulated other comprehensive loss (0.8) (0.8)
Shares in deferred compensation trust - 261,057 and 262,735 shares at a weighted average cost of $32.68 and $31.68 per share (8.5) (8.3)
Total common equity 3,116.0 3,013.0
Cumulative preferred stock (Interstate Power and Light Company) 145.1 145.1
Noncontrolling interest 1.7 1.8
Total equity 3,262.8 3,159.9
Cumulative preferred stock (Wisconsin Power and Light Company) 60.0 60.0
Long-term debt, net (excluding current portion) 2,828.1 2,703.1
Total capitalization 6,150.9 5,923.0
Current liabilities:    
Current maturities of long-term debt 1.4 1.4
Commercial paper 70.4 102.8
Accounts payable 418.0 267.8
Regulatory liabilities 168.5 164.7
Accrued taxes 37.4 46.9
Accrued interest 46.6 46.6
Derivative liabilities 37.8 55.9
Liabilities held for sale 66.1 62.1
Other 99.3 107.0
Total current liabilities 945.5 855.2
Other long-term liabilities and deferred credits:    
Deferred income tax liabilities 1,836.7 1,592.2
Regulatory liabilities 737.9 745.4
Pension and other benefit obligations 310.8 312.7
Other 269.1 259.4
Total long-term liabilities and deferred credits 3,154.5 2,909.7
Total capitalization and liabilities 10,250.9 9,687.9
IPL [Member]
    
Utility:    
Electric plant in service 4,767.4 4,684.0
Gas plant in service 436.9 428.2
Steam plant in service 34.9 34.9
Other plant in service 253.6 246.4
Accumulated depreciation (1,907.0) (1,833.8)
Net plant 3,585.8 3,559.7
Construction work in progress:    
George Neal Generating Station Units 3 and 4 emission controls (Interstate Power and Light Company) 53.5 8.3
Ottumwa Generating Station Unit 1 emission controls (Interstate Power and Light Company) 53.3 7.7
Other 87.4 80.6
Other, less accumulated depreciation 19.8 19.8
Non-regulated and other:    
Total property, plant and equipment 3,799.8 3,676.1
Current assets:    
Cash and cash equivalents 5.3 2.1
Accounts receivable:    
Customer, less allowance for doubtful accounts 183.4 75.2
Income tax refunds receivable 20.7 28.4
Production fuel, at weighted average cost 76.1 67.7
Materials and supplies, at weighted average cost 33.3 31.5
Gas stored underground, at weighted average cost 19.6 25.5
Regulatory assets 55.2 59.0
Derivative assets 25.9 9.2
Deferred income tax assets 35.9 13.5
Prepayments and other 11.9 11.0
Total current assets 467.3 323.1
Investments:    
Total investments 17.0 16.8
Other assets:    
Regulatory assets 1,095.8 1,058.3
Deferred charges and other 19.3 19.2
Total other assets 1,115.1 1,077.5
Total assets 5,399.2 5,093.5
Stockholders' Equity Attributable to Parent [Abstract]    
Common stock 33.4 33.4
Additional paid-in capital 1,007.8 927.7
Retained earnings 456.9 433.3
Total common equity 1,498.1 1,394.4
Cumulative preferred stock (Interstate Power and Light Company) 145.1 145.1
Total equity 1,643.2 1,539.5
Long-term debt, net (excluding current portion) 1,359.3 1,309.0
Total capitalization 3,002.5 2,848.5
Current liabilities:    
Commercial paper 0 7.1
Accounts payable 231.4 118.2
Accounts payable to associated companies 35.1 36.7
Regulatory liabilities 111.0 137.1
Accrued taxes 38.0 43.8
Accrued interest 22.9 22.8
Derivative liabilities 17.9 24.5
Other 34.2 32.3
Total current liabilities 490.5 422.5
Other long-term liabilities and deferred credits:    
Deferred income tax liabilities 1,039.4 936.9
Regulatory liabilities 577.1 584.2
Pension and other benefit obligations 99.8 101.9
Other 189.9 199.5
Total long-term liabilities and deferred credits 1,906.2 1,822.5
Total capitalization and liabilities 5,399.2 5,093.5
WPL [Member]
    
Utility:    
Electric plant in service 3,568.0 3,481.4
Gas plant in service 432.5 424.7
Other plant in service 224.0 228.8
Accumulated depreciation (1,444.5) (1,372.2)
Net plant 2,780.0 2,762.7
Leased Sheboygan Falls Energy Facility, less accumulated amortization 78.6 83.2
Construction work in progress:    
Edgewater Generating Station Unit 5 emission controls (Wisconsin Power and Light Company) 124.0 77.7
Columbia Energy Center Units 1 and 2 emission controls (Wisconsin Power and Light Company) 91.6 9.0
Other 71.7 73.9
Other, less accumulated depreciation 1.5 15.1
Non-regulated and other:    
Total property, plant and equipment 3,147.4 3,021.6
Current assets:    
Cash and cash equivalents 16.2 2.7
Accounts receivable:    
Customer, less allowance for doubtful accounts 84.6 76.2
Unbilled utility revenues 59.8 75.1
Other, less allowance for doubtful accounts 44.4 38.2
Income tax refunds receivable 23.0 0.7
Production fuel, at weighted average cost 34.4 34.2
Materials and supplies, at weighted average cost 26.7 25.7
Gas stored underground, at weighted average cost 17.7 32.2
Regulatory assets 37.7 44.6
Derivative assets 10.0 3.5
Prepaid gross receipts tax 29.1 40.2
Deferred income tax assets 50.3 6.0
Prepayments and other 20.8 6.7
Total current assets 454.7 386.0
Investments:    
Investment in American Transmission Company LLC 253.2 238.8
Other 19.3 19.8
Total investments 272.5 258.6
Other assets:    
Regulatory assets 329.7 333.1
Deferred charges and other 53.6 44.7
Total other assets 383.3 377.8
Total assets 4,257.9 4,044.0
Stockholders' Equity Attributable to Parent [Abstract]    
Common stock 66.2 66.2
Additional paid-in capital 869.2 869.0
Retained earnings 545.3 507.2
Total common equity 1,480.7 1,442.4
Cumulative preferred stock (Wisconsin Power and Light Company) 60.0 60.0
Long-term debt, net (excluding current portion) 1,082.5 1,082.2
Total capitalization 2,623.2 2,584.6
Current liabilities:    
Commercial paper 0 25.7
Accounts payable 133.5 98.5
Accounts payable to associated companies 20.5 20.5
Regulatory liabilities 57.5 27.6
Accrued interest 18.1 21.6
Derivative liabilities 19.9 31.4
Other 38.3 32.3
Total current liabilities 287.8 257.6
Other long-term liabilities and deferred credits:    
Deferred income tax liabilities 809.3 672.5
Regulatory liabilities 160.8 161.2
Capital lease obligations - Sheboygan Falls Energy Facility 100.2 103.3
Pension and other benefit obligations 127.8 128.0
Other 148.8 136.8
Total long-term liabilities and deferred credits 1,346.9 1,201.8
Total capitalization and liabilities $ 4,257.9 $ 4,044.0