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Segments Of Business (Schedule Of Segment Of Business) (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2015 | Sep. 30, 2015 | Jun. 30, 2015 | Mar. 31, 2015 | Dec. 31, 2014 | Sep. 30, 2014 | Jun. 30, 2014 | Mar. 31, 2014 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues | $ 740.1 | $ 898.9 | $ 717.2 | $ 897.4 | $ 804.1 | $ 843.1 | $ 750.3 | $ 952.8 | $ 3,253.6 | $ 3,350.3 | $ 3,276.8
Depreciation and amortization |  |  |  |  |  |  |  |  | 401.3 | 388.1 | 370.9
Operating income (loss) | 79.2 | 235.9 | 109.0 | 152.9 | 91.3 | 194.8 | 103.3 | 154.2 | 577.0 | 543.6 | 533.9
Interest expense |  |  |  |  |  |  |  |  | 187.1 | 180.6 | 172.8
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | (33.8) | (40.4) | (43.7)
Income tax expense (benefit) |  |  |  |  |  |  |  |  | 70.4 | 44.3 | 53.9
Net income (loss) attributable to common shareowners | 34.1 | 179.9 | 67.6 | 96.6 | 60.0 | 153.3 | 61.8 | 108.0 | 378.2 | 383.1 | 358.3
Total assets | 12,495.2 |  |  |  | 12,063.5 |  |  |  | 12,495.2 | 12,063.5 | 11,092.5
Investments in equity method subsidiaries | 302.9 |  |  |  | 296.6 |  |  |  | 302.9 | 296.6 | 281.4
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 1,034.3 | 902.8 | 798.3
IPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues | 398.7 | 504.6 | 382.2 | 489.0 | 431.1 | 476.2 | 411.9 | 528.9 | 1,774.5 | 1,848.1 | 1,818.8
Depreciation and amortization |  |  |  |  |  |  |  |  | 207.2 | 197.5 | 191.1
Operating income (loss) | 25.6 | 117.0 | 33.8 | 65.5 | 23.8 | 93.9 | 34.0 | 57.5 | 241.9 | 209.2 | 212.0
Interest expense |  |  |  |  |  |  |  |  | 96.8 | 89.9 | 81.3
Income tax expense (benefit) |  |  |  |  |  |  |  |  | (22.7) | (48.9) | (36.3)
Net income (loss) attributable to common shareowners | 5.5 | 116.5 | 16.5 | 47.5 | 18.9 | 102.0 | 18.0 | 42.7 | 186.0 | 181.6 | 172.0
Total assets | 6,709.1 |  |  |  | 6,450.2 |  |  |  | 6,709.1 | 6,450.2 |
WPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues | 330.7 | 382.6 | 324.7 | 397.1 | 359.8 | 354.4 | 324.5 | 410.4 | 1,435.1 | 1,449.1 | 1,406.3
Depreciation and amortization |  |  |  |  |  |  |  |  | 184.3 | 181.2 | 172.2
Operating income (loss) | 49.3 | 110.3 | 68.3 | 80.8 | 59.4 | 93.9 | 60.0 | 87.7 | 308.7 | 301.0 | 296.1
Interest expense |  |  |  |  |  |  |  |  | 92.4 | 86.4 | 85.0
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | (35.1) | (42.8) | (43.7)
Income tax expense (benefit) |  |  |  |  |  |  |  |  | 82.9 | 85.3 | 85.6
Net income (loss) attributable to common shareowners | 24.2 | $ 68.0 | $ 39.2 | $ 44.9 | 32.6 | $ 57.9 | $ 34.7 | $ 55.2 | 176.3 | 180.4 | 177.5
Total assets | 5,270.4 |  |  |  | 5,117.6 |  |  |  | 5,270.4 | 5,117.6 |
Electric [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 2,770.5 | 2,713.6 | 2,689.0
Depreciation and amortization |  |  |  |  |  |  |  |  | 358.6 | 347.0 | 333.0
Operating income (loss) |  |  |  |  |  |  |  |  | 514.1 | 442.4 | 444.5
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | (35.1) | (42.8) | (43.7)
Total assets | 10,211.3 |  |  |  | 9,660.4 |  |  |  | 10,211.3 | 9,660.4 | 9,018.6
Investments in equity method subsidiaries | 302.0 |  |  |  | 294.3 |  |  |  | 302.0 | 294.3 | 279.1
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 855.8 | 774.8 | 677.3
Electric [Member] | IPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 1,503.8 | 1,493.3 | 1,491.8
Depreciation and amortization |  |  |  |  |  |  |  |  | 187.9 | 178.7 | 173.1
Operating income (loss) |  |  |  |  |  |  |  |  | 218.8 | 166.8 | 173.1
Total assets | 5,754.1 |  |  |  | 5,398.3 |  |  |  | 5,754.1 | 5,398.3 | 4,905.3
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 561.2 | 490.0 | 365.4
Electric [Member] | WPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 1,266.7 | 1,220.3 | 1,197.2
Depreciation and amortization |  |  |  |  |  |  |  |  | 170.7 | 168.3 | 159.9
Operating income (loss) |  |  |  |  |  |  |  |  | 295.3 | 275.6 | 271.4
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | (35.1) | (42.8) | (43.7)
Total assets | 4,457.2 |  |  |  | 4,262.1 |  |  |  | 4,457.2 | 4,262.1 | 4,113.3
Investments in equity method subsidiaries | 302.0 |  |  |  | 294.3 |  |  |  | 302.0 | 294.3 | 279.1
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 294.6 | 284.8 | 311.9
Gas [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 381.2 | 517.5 | 464.8
Depreciation and amortization |  |  |  |  |  |  |  |  | 31.1 | 29.9 | 28.8
Operating income (loss) |  |  |  |  |  |  |  |  | 34.6 | 53.8 | 57.3
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | 0.0 | 0.0 | 0.0
Total assets | 939.3 |  |  |  | 913.5 |  |  |  | 939.3 | 913.5 | 859.3
Investments in equity method subsidiaries | 0.0 |  |  |  | 0.0 |  |  |  | 0.0 | 0.0 | 0.0
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 106.4 | 63.2 | 47.0
Gas [Member] | IPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 217.3 | 296.5 | 273.9
Depreciation and amortization |  |  |  |  |  |  |  |  | 17.5 | 17.0 | 16.5
Operating income (loss) |  |  |  |  |  |  |  |  | 17.7 | 25.7 | 29.8
Total assets | 548.2 |  |  |  | 544.1 |  |  |  | 548.2 | 544.1 | 518.8
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 56.7 | 35.1 | 27.5
Gas [Member] | WPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 163.9 | 221.0 | 190.9
Depreciation and amortization |  |  |  |  |  |  |  |  | 13.6 | 12.9 | 12.3
Operating income (loss) |  |  |  |  |  |  |  |  | 16.9 | 28.1 | 27.5
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | 0.0 | 0.0 | 0.0
Total assets | 391.1 |  |  |  | 369.4 |  |  |  | 391.1 | 369.4 | 340.5
Investments in equity method subsidiaries | 0.0 |  |  |  | 0.0 |  |  |  | 0.0 | 0.0 | 0.0
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 49.7 | 28.1 | 19.5
Other Utility [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 57.9 | 66.1 | 71.3
Depreciation and amortization |  |  |  |  |  |  |  |  | 1.8 | 1.8 | 1.5
Operating income (loss) |  |  |  |  |  |  |  |  | 1.9 | 14.0 | 6.3
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | 0.0 | 0.0 | 0.0
Total assets | 828.9 |  |  |  | 993.9 |  |  |  | 828.9 | 993.9 | 712.2
Investments in equity method subsidiaries | 0.0 |  |  |  | 0.0 |  |  |  | 0.0 | 0.0 | 0.0
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 1.4 | 0.9 | 7.3
Other Utility [Member] | IPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 53.4 | 58.3 | 53.1
Depreciation and amortization |  |  |  |  |  |  |  |  | 1.8 | 1.8 | 1.5
Operating income (loss) |  |  |  |  |  |  |  |  | 5.4 | 16.7 | 9.1
Total assets | 406.8 |  |  |  | 507.8 |  |  |  | 406.8 | 507.8 | 369.8
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 1.4 | 0.9 | 7.3
Other Utility [Member] | WPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 4.5 | 7.8 | 18.2
Depreciation and amortization |  |  |  |  |  |  |  |  | 0.0 | 0.0 | 0.0
Operating income (loss) |  |  |  |  |  |  |  |  | (3.5) | (2.7) | (2.8)
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | 0.0 | 0.0 | 0.0
Total assets | 422.1 |  |  |  | 486.1 |  |  |  | 422.1 | 486.1 | 342.4
Investments in equity method subsidiaries | 0.0 |  |  |  | 0.0 |  |  |  | 0.0 | 0.0 | 0.0
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 0.0 | 0.0 | 0.0
Utility Business [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 3,209.6 | 3,297.2 | 3,225.1
Depreciation and amortization |  |  |  |  |  |  |  |  | 391.5 | 378.7 | 363.3
Operating income (loss) |  |  |  |  |  |  |  |  | 550.6 | 510.2 | 508.1
Interest expense |  |  |  |  |  |  |  |  | 189.2 | 176.3 | 166.3
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | (35.1) | (42.8) | (43.7)
Income tax expense (benefit) |  |  |  |  |  |  |  |  | 60.2 | 36.4 | 49.3
Net income (loss) attributable to common shareowners |  |  |  |  |  |  |  |  | 362.3 | 362.0 | 349.5
Total assets | 11,979.5 |  |  |  | 11,567.8 |  |  |  | 11,979.5 | 11,567.8 | 10,590.1
Investments in equity method subsidiaries | 302.0 |  |  |  | 294.3 |  |  |  | 302.0 | 294.3 | 279.1
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 963.6 | 838.9 | 731.6
Utility Business [Member] | IPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 1,774.5 | 1,848.1 | 1,818.8
Depreciation and amortization |  |  |  |  |  |  |  |  | 207.2 | 197.5 | 191.1
Operating income (loss) |  |  |  |  |  |  |  |  | 241.9 | 209.2 | 212.0
Interest expense |  |  |  |  |  |  |  |  | 96.8 | 89.9 | 81.3
Income tax expense (benefit) |  |  |  |  |  |  |  |  | (22.7) | (48.9) | (36.3)
Net income (loss) attributable to common shareowners |  |  |  |  |  |  |  |  | 186.0 | 181.6 | 172.0
Total assets | 6,709.1 |  |  |  | 6,450.2 |  |  |  | 6,709.1 | 6,450.2 | 5,793.9
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 619.3 | 526.0 | 400.2
Utility Business [Member] | WPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 1,435.1 | 1,449.1 | 1,406.3
Depreciation and amortization |  |  |  |  |  |  |  |  | 184.3 | 181.2 | 172.2
Operating income (loss) |  |  |  |  |  |  |  |  | 308.7 | 301.0 | 296.1
Interest expense |  |  |  |  |  |  |  |  | 92.4 | 86.4 | 85.0
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | (35.1) | (42.8) | (43.7)
Income tax expense (benefit) |  |  |  |  |  |  |  |  | 82.9 | 85.3 | 85.6
Net income (loss) attributable to common shareowners |  |  |  |  |  |  |  |  | 176.3 | 180.4 | 177.5
Total assets | 5,270.4 |  |  |  | 5,117.6 |  |  |  | 5,270.4 | 5,117.6 | 4,796.2
Investments in equity method subsidiaries | 302.0 |  |  |  | 294.3 |  |  |  | 302.0 | 294.3 | 279.1
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 344.3 | 312.9 | 331.4
Non-Regulated [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 44.0 | 53.1 | 51.7
Depreciation and amortization |  |  |  |  |  |  |  |  | 9.8 | 9.4 | 7.6
Operating income (loss) |  |  |  |  |  |  |  |  | 26.4 | 33.4 | 25.8
Interest (income) expense |  |  |  |  |  |  |  |  | (2.1) | 4.3 | 6.5
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | 1.3 | 2.4 | 0.0
Income tax expense (benefit) |  |  |  |  |  |  |  |  | 10.2 | 7.9 | 4.6
Net income (loss) attributable to common shareowners |  |  |  |  |  |  |  |  | 15.9 | 21.1 | 8.8
Total assets | 515.7 |  |  |  | 495.7 |  |  |  | 515.7 | 495.7 | 502.4
Investments in equity method subsidiaries | $ 0.9 |  |  |  | $ 2.3 |  |  |  | 0.9 | 2.3 | 2.3
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | $ 70.7 | $ 63.9 | $ 66.7

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