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Segments Of Business (Tables)
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12 Months Ended |
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Dec. 31, 2012
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| Segment Reporting Information [Line Items] |
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| Schedule of Segments of Business |
Certain financial information relating to Alliant Energy’s business segments, products and services and geographic information was as follows (in millions): | | | | | | | | | | | | | | | | | | | | | | | | | | Utility | | Non-Regulated, | | Alliant Energy | 2012 | Electric | | Gas | | Other | | Total | | Parent and Other | | Consolidated | Operating revenues |
| $2,589.3 |
| |
| $396.3 |
| |
| $56.7 |
| |
| $3,042.3 |
| |
| $52.2 |
| |
| $3,094.5 |
| Depreciation and amortization | 299.3 |
| | 29.1 |
| | 1.4 |
| | 329.8 |
| | 2.6 |
| | 332.4 |
| Operating income | 426.2 |
| | 51.5 |
| | 7.4 |
| | 485.1 |
| | 34.6 |
| | 519.7 |
| Interest expense, net of AFUDC | | | | | | | 136.8 |
| | (2.0 | ) | | 134.8 |
| Equity (income) loss from unconsolidated investments, net | (42.1 | ) | | — |
| | — |
| | (42.1 | ) | | 0.8 |
| | (41.3 | ) | Interest income and other | | | | | | | (0.3 | ) | | (3.7 | ) | | (4.0 | ) | Income taxes | | | | | | | 74.8 |
| | 14.6 |
| | 89.4 |
| Income from continuing operations, net of tax | | | | | | | 315.9 |
| | 24.9 |
| | 340.8 |
| Loss from discontinued operations, net of tax | | | | | | | — |
| | (5.1 | ) | | (5.1 | ) | Net income | | | | | | | 315.9 |
| | 19.8 |
| | 335.7 |
| Preferred dividends | | | | | | | 15.9 |
| | — |
| | 15.9 |
| Net income attributable to Alliant Energy common shareowners | | | | | | | 300.0 |
| | 19.8 |
| | 319.8 |
| Total assets | 8,438.8 |
| | 814.8 |
| | 966.0 |
| | 10,219.6 |
| | 565.9 |
| | 10,785.5 |
| Investments in equity method subsidiaries | 264.3 |
| | — |
| | — |
| | 264.3 |
| | 2.3 |
| | 266.6 |
| Construction and acquisition expenditures | 994.0 |
| | 31.4 |
| | 0.1 |
| | 1,025.5 |
| | 132.6 |
| | 1,158.1 |
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| | | | | | | | | | | | | | | | | | | | | | | | | | Utility | | Non-Regulated, | | Alliant Energy | 2011 | Electric | | Gas | | Other | | Total | | Parent and Other | | Consolidated | Operating revenues |
| $2,635.8 |
| |
| $476.7 |
| |
| $62.0 |
| |
| $3,174.5 |
| |
| $46.9 |
| |
| $3,221.4 |
| Depreciation and amortization | 289.0 |
| | 28.4 |
| | 1.8 |
| | 319.2 |
| | 1.8 |
| | 321.0 |
| Operating income (loss) | 444.2 |
| | 47.8 |
| | (3.2 | ) | | 488.8 |
| | 24.5 |
| | 513.3 |
| Interest expense, net of AFUDC | | | | | | | 146.6 |
| | (0.3 | ) | | 146.3 |
| Equity income from unconsolidated investments, net | (38.7 | ) | | — |
| | — |
| | (38.7 | ) | | (0.6 | ) | | (39.3 | ) | Interest income and other | | | | | | | (0.2 | ) | | (4.1 | ) | | (4.3 | ) | Income tax expense (benefit) | | | | | | | 78.3 |
| | (9.1 | ) | | 69.2 |
| Income from continuing operations, net of tax | | | | | | | 302.8 |
| | 38.6 |
| | 341.4 |
| Loss from discontinued operations, net of tax | | | | | | | — |
| | (19.5 | ) | | (19.5 | ) | Net income | | | | | | | 302.8 |
| | 19.1 |
| | 321.9 |
| Preferred dividends | | | | | | | 18.3 |
| | — |
| | 18.3 |
| Net income attributable to Alliant Energy common shareowners | | | | | | | 284.5 |
| | 19.1 |
| | 303.6 |
| Total assets | 7,524.5 |
| | 831.9 |
| | 781.1 |
| | 9,137.5 |
| | 550.4 |
| | 9,687.9 |
| Investments in equity method subsidiaries | 246.5 |
| | — |
| | — |
| | 246.5 |
| | 3.1 |
| | 249.6 |
| Construction and acquisition expenditures | 542.7 |
| | 38.0 |
| | 27.4 |
| | 608.1 |
| | 65.3 |
| | 673.4 |
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| | | | | | | | | | | | | | | | | | | | | | | | | | Utility | | Non-Regulated, | | Alliant Energy | 2010 | Electric | | Gas | | Other | | Total | | Parent and Other | | Consolidated | Operating revenues |
| $2,674.2 |
| |
| $480.6 |
| |
| $64.6 |
| |
| $3,219.4 |
| |
| $42.7 |
| |
| $3,262.1 |
| Depreciation and amortization | 255.1 |
| | 25.2 |
| | 5.3 |
| | 285.6 |
| | 1.7 |
| | 287.3 |
| Operating income (loss) | 489.8 |
| | 53.4 |
| | (2.5 | ) | | 540.7 |
| | 19.3 |
| | 560.0 |
| Interest expense, net of AFUDC | | | | | | | 142.8 |
| | 2.0 |
| | 144.8 |
| Equity income from unconsolidated investments, net | (37.8 | ) | | — |
| | — |
| | (37.8 | ) | | (0.3 | ) | | (38.1 | ) | Interest income and other | | | | | | | (0.6 | ) | | (4.0 | ) | | (4.6 | ) | Income taxes | | | | | | | 140.6 |
| | 7.1 |
| | 147.7 |
| Income from continuing operations, net of tax | | | | | | | 295.7 |
| | 14.5 |
| | 310.2 |
| Loss from discontinued operations, net of tax | | | | | | | — |
| | (3.9 | ) | | (3.9 | ) | Net income | | | | | | | 295.7 |
| | 10.6 |
| | 306.3 |
| Preferred dividends | | | | | | | 18.7 |
| | — |
| | 18.7 |
| Net income attributable to Alliant Energy common shareowners | | | | | | | 277.0 |
| | 10.6 |
| | 287.6 |
| Total assets | 7,227.2 |
| | 817.6 |
| | 782.4 |
| | 8,827.2 |
| | 455.7 |
| | 9,282.9 |
| Investments in equity method subsidiaries | 236.0 |
| | — |
| | — |
| | 236.0 |
| | 2.5 |
| | 238.5 |
| Construction and acquisition expenditures | 729.1 |
| | 39.9 |
| | 64.3 |
| | 833.3 |
| | 33.6 |
| | 866.9 |
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| Schedule of Products and Services |
Products and Services - Alliant Energy’s consolidated operating revenues by segment were as follows: | | | | | | | | | | | 2012 | | 2011 | | 2010 | Utility electric operations | 84 | % | | 82 | % | | 82 | % | Utility gas operations | 13 | % | | 15 | % | | 15 | % | Utility other | 2 | % | | 2 | % | | 2 | % | Other | 1 | % | | 1 | % | | 1 | % | | 100 | % | | 100 | % | | 100 | % |
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IPL [Member]
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| Segment Reporting Information [Line Items] |
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| Schedule of Segments of Business |
Certain financial information relating to IPL’s business segments was as follows (in millions): | | | | | | | | | | | | | | | | | 2012 | Electric | | Gas | | Other | | Total | Operating revenues |
| $1,371.1 |
| |
| $226.7 |
| |
| $52.5 |
| |
| $1,650.3 |
| Depreciation and amortization | 171.2 |
| | 16.3 |
| | 1.4 |
| | 188.9 |
| Operating income | 166.2 |
| | 24.2 |
| | 9.9 |
| | 200.3 |
| Interest expense, net of AFUDC | | | | | | | 70.1 |
| Interest income and other | | | | | | | (0.2 | ) | Income tax benefit | | | | | | | (19.8 | ) | Net income | | | | | | | 150.2 |
| Preferred dividends | | | | | | | 12.6 |
| Earnings available for common stock | | | | | | | 137.6 |
| Total assets | 4,500.9 |
| | 479.5 |
| | 476.6 |
| | 5,457.0 |
| Construction and acquisition expenditures | 291.0 |
| | 16.4 |
| | 0.1 |
| | 307.5 |
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| | | | | | | | | | | | | | | | | 2011 | Electric | | Gas | | Other | | Total | Operating revenues |
| $1,408.3 |
| |
| $276.3 |
| |
| $55.5 |
| |
| $1,740.1 |
| Depreciation and amortization | 161.3 |
| | 16.0 |
| | 1.8 |
| | 179.1 |
| Operating income | 181.6 |
| | 20.6 |
| | 6.2 |
| | 208.4 |
| Interest expense, net of AFUDC | | | | | | | 72.9 |
| Interest income and other | | | | | | | (0.2 | ) | Income tax benefit | | | | | | | (3.6 | ) | Net income | | | | | | | 139.3 |
| Preferred dividends | | | | | | | 15.0 |
| Earnings available for common stock | | | | | | | 124.3 |
| Total assets | 4,208.2 |
| | 471.1 |
| | 414.2 |
| | 5,093.5 |
| Construction and acquisition expenditures | 245.6 |
| | 21.2 |
| | 26.9 |
| | 293.7 |
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| | | | | | | | | | | | | | | | 2010 | Electric | | Gas | | Other | | Total | Operating revenues |
| $1,464.3 |
| |
| $274.3 |
| |
| $57.2 |
| | $1,795.8 | Depreciation and amortization | 157.1 |
| | 14.6 |
| | 5.3 |
| | 177.0 |
| Operating income (loss) | 239.7 |
| | 23.6 |
| | (1.4 | ) | | 261.9 |
| Interest expense, net of AFUDC | | | | | | | 76.7 |
| Interest income and other | | | | | | | (0.5 | ) | Income taxes | | | | | | | 42.3 |
| Net income | | | | | | | 143.4 |
| Preferred dividends | | | | | | | 15.4 |
| Earnings available for common stock | | | | | | | 128.0 |
| Total assets | 4,025.3 |
| | 460.3 |
| | 452.0 |
| | 4,937.6 |
| Construction and acquisition expenditures | 298.8 |
| | 20.0 |
| | 64.0 |
| | 382.8 |
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WPL [Member]
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| Segment Reporting Information [Line Items] |
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| Schedule of Segments of Business |
Certain financial information relating to WPL’s business segments was as follows (in millions): | | | | | | | | | | | | | | | | | 2012 | Electric | | Gas | | Other | | Total | Operating revenues |
| $1,218.2 |
| |
| $169.6 |
| |
| $4.2 |
| |
| $1,392.0 |
| Depreciation and amortization | 128.1 |
| | 12.8 |
| | — |
| | 140.9 |
| Operating income (loss) | 260.0 |
| | 27.3 |
| | (2.5 | ) | | 284.8 |
| Interest expense, net of AFUDC | | | | | | | 66.7 |
| Equity income from unconsolidated investments | (42.1 | ) | | — |
| | — |
| | (42.1 | ) | Interest income and other | | | | | | | (0.1 | ) | Income taxes | | | | | | | 94.6 |
| Net income | | | | | | | 165.7 |
| Preferred dividends | | | | | | | 3.3 |
| Earnings available for common stock | | | | | | | 162.4 |
| Total assets | 3,937.9 |
| | 335.3 |
| | 489.4 |
| | 4,762.6 |
| Investments in equity method subsidiaries | 264.3 |
| | — |
| | — |
| | 264.3 |
| Construction and acquisition expenditures | 703.0 |
| | 15.0 |
| | — |
| | 718.0 |
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| | | | | | | | | | | | | | | 2011 | Electric | | Gas | | Other | | Total | Operating revenues | $1,227.5 | |
| $200.4 |
| |
| $6.5 |
| |
| $1,434.4 |
| Depreciation and amortization | 127.7 | | 12.4 | | — | | 140.1 |
| Operating income (loss) | 262.6 | | 27.2 | | (9.4) | | 280.4 |
| Interest expense, net of AFUDC | | | | | | | 73.7 |
| Equity income from unconsolidated investments | (38.7) | | — | | — | | (38.7 | ) | Income taxes | | | | | | | 81.9 |
| Net income | | | | | | | 163.5 |
| Preferred dividends | | | | | | | 3.3 |
| Earnings available for common stock | | | | | | | 160.2 |
| Total assets | 3,316.3 | | 360.8 | | 366.9 | | 4,044.0 |
| Investments in equity method subsidiaries | 246.5 | | — | | — | | 246.5 |
| Construction and acquisition expenditures | 297.1 | | 16.8 | | 0.5 | | 314.4 |
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| | | | | | | | | | | | | | | 2010 | Electric | | Gas | | Other | | Total | Operating revenues | $1,209.9 | |
| $206.3 |
| |
| $7.4 |
| |
| $1,423.6 |
| Depreciation and amortization | 98.0 | | 10.6 | | — | | 108.6 |
| Operating income (loss) | 250.1 | | 29.8 | | (1.1) | | 278.8 |
| Interest expense, net of AFUDC | | | | | | | 66.1 |
| Equity income from unconsolidated investments | (37.8) | | — | | — | | (37.8 | ) | Interest income and other | | | | | | | (0.1 | ) | Income taxes | | | | | | | 98.3 |
| Net income | | | | | | | 152.3 |
| Preferred dividends | | | | | | | 3.3 |
| Earnings available for common stock | | | | | | | 149.0 |
| Total assets | 3,201.9 | | 357.3 | | 330.4 | | 3,889.6 |
| Investments in equity method subsidiaries | 236.0 | | — | | — | | 236.0 |
| Construction and acquisition expenditures | 430.3 | | 19.9 |
| | 0.3 |
| | 450.5 |
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|