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Segments Of Business (Schedule Of Segment Of Business) (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2016 | Sep. 30, 2016 | Jun. 30, 2016 | Mar. 31, 2016 | Dec. 31, 2015 | Sep. 30, 2015 | Jun. 30, 2015 | Mar. 31, 2015 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues | $ 797.0 | $ 924.6 | $ 754.6 | $ 843.8 | $ 740.1 | $ 898.9 | $ 717.2 | $ 897.4 | $ 3,320.0 | $ 3,253.6 | $ 3,350.3
Depreciation and amortization |  |  |  |  |  |  |  |  | 411.6 | 401.3 | 388.1
Operating income (loss) | 99.9 | 162.6 | 128.6 | 145.9 | 79.2 | 235.9 | 109.0 | 152.9 | 537.0 | 577.0 | 543.6
Interest expense |  |  |  |  |  |  |  |  | 196.2 | 187.1 | 180.6
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | (39.6) | (33.8) | (40.4)
Income tax expense (benefit) |  |  |  |  |  |  |  |  | 59.4 | 70.4 | 44.3
Net income (loss) attributable to common shareowners | 62.7 | 128.4 | 83.9 | 96.5 | 34.1 | 179.9 | 67.6 | 96.6 | 371.5 | 378.2 | 383.1
Total assets | 13,373.8 |  |  |  | 12,495.2 |  |  |  | 13,373.8 | 12,495.2 | 12,063.5
Investments in equity method subsidiaries | 326.0 |  |  |  | 302.9 |  |  |  | 326.0 | 302.9 | 296.6
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 1,196.8 | 1,034.3 | 902.8
IPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues | 434.5 | 516.2 | 411.0 | 458.7 | 398.7 | 504.6 | 382.2 | 489.0 | 1,820.4 | 1,774.5 | 1,848.1
Depreciation and amortization |  |  |  |  |  |  |  |  | 210.8 | 207.2 | 197.5
Operating income (loss) | 34.9 | 125.9 | 48.0 | 62.0 | 25.6 | 117.0 | 33.8 | 65.5 | 270.8 | 241.9 | 209.2
Interest expense |  |  |  |  |  |  |  |  | 103.2 | 96.8 | 89.9
Income tax expense (benefit) |  |  |  |  |  |  |  |  | (5.9) | (22.7) | (48.9)
Net income (loss) attributable to common shareowners | 24.0 | 114.1 | 31.9 | 45.6 | 5.5 | 116.5 | 16.5 | 47.5 | 215.6 | 186.0 | 181.6
Total assets | 7,304.7 |  |  |  | 6,709.1 |  |  |  | 7,304.7 | 6,709.1 |
WPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues | 352.2 | 397.0 | 334.3 | 375.6 | 330.7 | 382.6 | 324.7 | 397.1 | 1,459.1 | 1,435.1 | 1,449.1
Depreciation and amortization |  |  |  |  |  |  |  |  | 192.5 | 184.3 | 181.2
Operating income (loss) | 58.2 | 115.0 | 75.0 | 78.8 | 49.3 | 110.3 | 68.3 | 80.8 | 327.0 | 308.7 | 301.0
Interest expense |  |  |  |  |  |  |  |  | 91.4 | 92.4 | 86.4
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | (39.8) | (35.1) | (42.8)
Income tax expense (benefit) |  |  |  |  |  |  |  |  | 93.3 | 82.9 | 85.3
Net income (loss) attributable to common shareowners | 31.7 | $ 69.0 | $ 43.2 | $ 46.5 | 24.2 | $ 68.0 | $ 39.2 | $ 44.9 | 190.4 | 176.3 | 180.4
Total assets | 5,290.3 |  |  |  | 5,270.4 |  |  |  | 5,290.3 | 5,270.4 |
Electric [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 2,875.5 | 2,770.5 | 2,713.6
Depreciation and amortization |  |  |  |  |  |  |  |  | 367.0 | 358.6 | 347.0
Operating income (loss) |  |  |  |  |  |  |  |  | 571.9 | 514.1 | 442.4
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | (39.8) | (35.1) | (42.8)
Total assets | 11,040.5 |  |  |  | 10,211.3 |  |  |  | 11,040.5 | 10,211.3 | 9,660.4
Investments in equity method subsidiaries | 325.3 |  |  |  | 302.0 |  |  |  | 325.3 | 302.0 | 294.3
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 1,005.5 | 855.8 | 774.8
Electric [Member] | IPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 1,569.7 | 1,503.8 | 1,493.3
Depreciation and amortization |  |  |  |  |  |  |  |  | 189.4 | 187.9 | 178.7
Operating income (loss) |  |  |  |  |  |  |  |  | 252.0 | 218.8 | 166.8
Total assets | 6,278.2 |  |  |  | 5,754.1 |  |  |  | 6,278.2 | 5,754.1 | 5,398.3
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 598.1 | 561.2 | 490.0
Electric [Member] | WPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 1,305.8 | 1,266.7 | 1,220.3
Depreciation and amortization |  |  |  |  |  |  |  |  | 177.6 | 170.7 | 168.3
Operating income (loss) |  |  |  |  |  |  |  |  | 319.9 | 295.3 | 275.6
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | (39.8) | (35.1) | (42.8)
Total assets | 4,444.7 |  |  |  | 4,457.2 |  |  |  | 4,444.7 | 4,457.2 | 4,262.1
Investments in equity method subsidiaries | 7.7 |  |  |  | 302.0 |  |  |  | 7.7 | 302.0 | 294.3
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 407.4 | 294.6 | 284.8
Gas [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 355.4 | 381.2 | 517.5
Depreciation and amortization |  |  |  |  |  |  |  |  | 34.2 | 31.1 | 29.9
Operating income (loss) |  |  |  |  |  |  |  |  | 30.7 | 34.6 | 53.8
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | 0.0 | 0.0 | 0.0
Total assets | 1,091.1 |  |  |  | 939.3 |  |  |  | 1,091.1 | 939.3 | 913.5
Investments in equity method subsidiaries | 0.0 |  |  |  | 0.0 |  |  |  | 0.0 | 0.0 | 0.0
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 137.1 | 106.4 | 63.2
Gas [Member] | IPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 204.0 | 217.3 | 296.5
Depreciation and amortization |  |  |  |  |  |  |  |  | 19.3 | 17.5 | 17.0
Operating income (loss) |  |  |  |  |  |  |  |  | 15.5 | 17.7 | 25.7
Total assets | 653.3 |  |  |  | 548.2 |  |  |  | 653.3 | 548.2 | 544.1
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 91.5 | 56.7 | 35.1
Gas [Member] | WPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 151.4 | 163.9 | 221.0
Depreciation and amortization |  |  |  |  |  |  |  |  | 14.9 | 13.6 | 12.9
Operating income (loss) |  |  |  |  |  |  |  |  | 15.2 | 16.9 | 28.1
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | 0.0 | 0.0 | 0.0
Total assets | 437.8 |  |  |  | 391.1 |  |  |  | 437.8 | 391.1 | 369.4
Investments in equity method subsidiaries | 0.0 |  |  |  | 0.0 |  |  |  | 0.0 | 0.0 | 0.0
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 45.6 | 49.7 | 28.1
Other Utility [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 48.6 | 57.9 | 66.1
Depreciation and amortization |  |  |  |  |  |  |  |  | 2.1 | 1.8 | 1.8
Operating income (loss) |  |  |  |  |  |  |  |  | (4.8) | 1.9 | 14.0
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | 0.0 | 0.0 | 0.0
Total assets | 781.0 |  |  |  | 828.9 |  |  |  | 781.0 | 828.9 | 993.9
Investments in equity method subsidiaries | 0.0 |  |  |  | 0.0 |  |  |  | 0.0 | 0.0 | 0.0
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 0.1 | 1.4 | 0.9
Other Utility [Member] | IPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 46.7 | 53.4 | 58.3
Depreciation and amortization |  |  |  |  |  |  |  |  | 2.1 | 1.8 | 1.8
Operating income (loss) |  |  |  |  |  |  |  |  | 3.3 | 5.4 | 16.7
Total assets | 373.2 |  |  |  | 406.8 |  |  |  | 373.2 | 406.8 | 507.8
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 0.1 | 1.4 | 0.9
Other Utility [Member] | WPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 1.9 | 4.5 | 7.8
Depreciation and amortization |  |  |  |  |  |  |  |  | 0.0 | 0.0 | 0.0
Operating income (loss) |  |  |  |  |  |  |  |  | (8.1) | (3.5) | (2.7)
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | 0.0 | 0.0 | 0.0
Total assets | 407.8 |  |  |  | 422.1 |  |  |  | 407.8 | 422.1 | 486.1
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 |  |  |  |  |  |  |  |  | 3,279.5 | 3,209.6 | 3,297.2
Depreciation and amortization |  |  |  |  |  |  |  |  | 403.3 | 391.5 | 378.7
Operating income (loss) |  |  |  |  |  |  |  |  | 597.8 | 550.6 | 510.2
Interest expense |  |  |  |  |  |  |  |  | 194.6 | 189.2 | 176.3
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | (39.8) | (35.1) | (42.8)
Income tax expense (benefit) |  |  |  |  |  |  |  |  | 87.4 | 60.2 | 36.4
Net income (loss) attributable to common shareowners |  |  |  |  |  |  |  |  | 406.0 | 362.3 | 362.0
Total assets | 12,912.6 |  |  |  | 11,979.5 |  |  |  | 12,912.6 | 11,979.5 | 11,567.8
Investments in equity method subsidiaries | 325.3 |  |  |  | 302.0 |  |  |  | 325.3 | 302.0 | 294.3
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 1,142.7 | 963.6 | 838.9
Utility Business [Member] | IPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 1,820.4 | 1,774.5 | 1,848.1
Depreciation and amortization |  |  |  |  |  |  |  |  | 210.8 | 207.2 | 197.5
Operating income (loss) |  |  |  |  |  |  |  |  | 270.8 | 241.9 | 209.2
Interest expense |  |  |  |  |  |  |  |  | 103.2 | 96.8 | 89.9
Income tax expense (benefit) |  |  |  |  |  |  |  |  | (5.9) | (22.7) | (48.9)
Net income (loss) attributable to common shareowners |  |  |  |  |  |  |  |  | 215.6 | 186.0 | 181.6
Total assets | 7,304.7 |  |  |  | 6,709.1 |  |  |  | 7,304.7 | 6,709.1 | 6,450.2
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 689.7 | 619.3 | 526.0
Utility Business [Member] | WPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 1,459.1 | 1,435.1 | 1,449.1
Depreciation and amortization |  |  |  |  |  |  |  |  | 192.5 | 184.3 | 181.2
Operating income (loss) |  |  |  |  |  |  |  |  | 327.0 | 308.7 | 301.0
Interest expense |  |  |  |  |  |  |  |  | 91.4 | 92.4 | 86.4
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | (39.8) | (35.1) | (42.8)
Income tax expense (benefit) |  |  |  |  |  |  |  |  | 93.3 | 82.9 | 85.3
Net income (loss) attributable to common shareowners |  |  |  |  |  |  |  |  | 190.4 | 176.3 | 180.4
Total assets | 5,290.3 |  |  |  | 5,270.4 |  |  |  | 5,290.3 | 5,270.4 | 5,117.6
Investments in equity method subsidiaries | 7.7 |  |  |  | 302.0 |  |  |  | 7.7 | 302.0 | 294.3
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 453.0 | 344.3 | 312.9
Non-Regulated [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 40.5 | 44.0 | 53.1
Depreciation and amortization |  |  |  |  |  |  |  |  | 8.3 | 9.8 | 9.4
Operating income (loss) |  |  |  |  |  |  |  |  | (60.8) | 26.4 | 33.4
Interest expense |  |  |  |  |  |  |  |  | 1.6 |  | 4.3
Interest income |  |  |  |  |  |  |  |  |  | (2.1) |
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | 0.2 | 1.3 | 2.4
Income tax expense (benefit) |  |  |  |  |  |  |  |  | (28.0) | 10.2 | 7.9
Net income (loss) attributable to common shareowners |  |  |  |  |  |  |  |  | (34.5) | 15.9 | 21.1
Total assets | 461.2 |  |  |  | 515.7 |  |  |  | 461.2 | 515.7 | 495.7
Investments in equity method subsidiaries | $ 0.7 |  |  |  | $ 0.9 |  |  |  | 0.7 | 0.9 | 2.3
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | $ 54.1 | $ 70.7 | $ 63.9

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