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Segments Of Business (Schedule Of Segment Of Business) (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2016 | Sep. 30, 2016 | Jun. 30, 2016 | Mar. 31, 2016 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues | $ 856.1 | $ 906.9 | $ 765.3 | $ 853.9 | $ 797.0 | $ 924.6 | $ 754.6 | $ 843.8 | $ 3,382.2 | $ 3,320.0 | $ 3,253.6
Depreciation and amortization |  |  |  |  |  |  |  |  | 461.8 | 411.6 | 401.3
Operating income (loss) | 129.7 | 231.5 | 149.3 | 142.9 | 99.9 | 162.6 | 128.6 | 145.9 | 653.4 | 537.0 | 577.0
Interest expense |  |  |  |  |  |  |  |  | 215.6 | 196.2 | 187.1
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | (44.8) | (39.6) | (33.8)
Income tax expense (benefit) |  |  |  |  |  |  |  |  | 66.7 | 59.4 | 70.4
Net income (loss) attributable to common shareowners | 93.8 | 168.8 | 94.3 | 100.4 | 62.7 | 128.4 | 83.9 | 96.5 | 457.3 | 371.5 | 378.2
Total assets | 14,187.8 |  |  |  | 13,373.8 |  |  |  | 14,187.8 | 13,373.8 | 12,495.2
Investments in equity method subsidiaries | 381.4 |  |  |  | 326.0 |  |  |  | 381.4 | 326.0 | 302.9
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 1,466.9 | 1,196.8 | 1,034.3
IPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues | 472.2 | 527.4 | 420.2 | 450.5 | 434.5 | 516.2 | 411.0 | 458.7 | 1,870.3 | 1,820.4 | 1,774.5
Depreciation and amortization |  |  |  |  |  |  |  |  | 245.0 | 210.8 | 207.2
Operating income (loss) | 49.2 | 131.8 | 66.3 | 49.6 | 34.9 | 125.9 | 48.0 | 62.0 | 296.9 | 270.8 | 241.9
Interest expense |  |  |  |  |  |  |  |  | 112.4 | 103.2 | 96.8
Income tax expense (benefit) |  |  |  |  |  |  |  |  | (10.9) | (5.9) | (22.7)
Net income (loss) attributable to common shareowners | 16.4 | 120.4 | 42.8 | 37.2 | 24.0 | 114.1 | 31.9 | 45.6 | 216.8 | 215.6 | 186.0
Total assets | 7,606.0 |  |  |  | 7,304.7 |  |  |  | 7,606.0 | 7,304.7 |
WPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues | 374.7 | 370.2 | 334.8 | 393.1 | 352.2 | 397.0 | 334.3 | 375.6 | 1,472.8 | 1,459.1 | 1,435.1
Depreciation and amortization |  |  |  |  |  |  |  |  | 212.9 | 192.5 | 184.3
Operating income (loss) | 72.8 | 90.7 | 73.7 | 86.0 | 58.2 | 115.0 | 75.0 | 78.8 | 323.2 | 327.0 | 308.7
Interest expense |  |  |  |  |  |  |  |  | 93.8 | 91.4 | 92.4
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | (0.7) | (39.8) | (35.1)
Income tax expense (benefit) |  |  |  |  |  |  |  |  | 61.9 | 93.3 | 82.9
Net income (loss) attributable to common shareowners | 53.2 | $ 49.8 | $ 38.1 | $ 45.5 | 31.7 | $ 69.0 | $ 43.2 | $ 46.5 | 186.6 | 190.4 | 176.3
Total assets | 5,756.5 |  |  |  | 5,290.3 |  |  |  | 5,756.5 | 5,290.3 |
Electric [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 2,894.7 | 2,875.5 | 2,770.5
Depreciation and amortization |  |  |  |  |  |  |  |  | 412.0 | 367.0 | 358.6
Operating income (loss) |  |  |  |  |  |  |  |  | 586.5 | 571.9 | 514.1
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | (0.7) | (0.7) | (0.9)
Total assets | 11,396.2 |  |  |  | 10,722.9 |  |  |  | 11,396.2 | 10,722.9 | 9,918.0
Investments in equity method subsidiaries | 8.3 |  |  |  | 7.7 |  |  |  | 8.3 | 7.7 | 8.7
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 1,154.9 | 994.0 | 852.5
Electric [Member] | IPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 1,598.9 | 1,569.7 | 1,503.8
Depreciation and amortization |  |  |  |  |  |  |  |  | 215.1 | 189.4 | 187.9
Operating income (loss) |  |  |  |  |  |  |  |  | 281.1 | 252.0 | 218.8
Total assets | 6,524.4 |  |  |  | 6,278.2 |  |  |  | 6,524.4 | 6,278.2 | 5,754.1
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 594.1 | 598.1 | 561.2
Electric [Member] | WPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 1,295.8 | 1,305.8 | 1,266.7
Depreciation and amortization |  |  |  |  |  |  |  |  | 196.9 | 177.6 | 170.7
Operating income (loss) |  |  |  |  |  |  |  |  | 305.4 | 319.9 | 295.3
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | (0.7) | (0.7) | (0.9)
Total assets | 4,871.8 |  |  |  | 4,444.7 |  |  |  | 4,871.8 | 4,444.7 | 4,163.9
Investments in equity method subsidiaries | 8.3 |  |  |  | 7.7 |  |  |  | 8.3 | 7.7 | 8.7
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 592.4 | 395.9 | 291.3
Gas [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 400.9 | 355.4 | 381.2
Depreciation and amortization |  |  |  |  |  |  |  |  | 38.2 | 34.2 | 31.1
Operating income (loss) |  |  |  |  |  |  |  |  | 45.3 | 30.7 | 34.6
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | 0.0 | 0.0 | 0.0
Total assets | 1,199.8 |  |  |  | 1,091.1 |  |  |  | 1,199.8 | 1,091.1 | 939.3
Investments in equity method subsidiaries | 0.0 |  |  |  | 0.0 |  |  |  | 0.0 | 0.0 | 0.0
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 125.2 | 137.1 | 106.4
Gas [Member] | IPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 226.0 | 204.0 | 217.3
Depreciation and amortization |  |  |  |  |  |  |  |  | 22.2 | 19.3 | 17.5
Operating income (loss) |  |  |  |  |  |  |  |  | 20.8 | 15.5 | 17.7
Total assets | 727.9 |  |  |  | 653.3 |  |  |  | 727.9 | 653.3 | 548.2
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 80.7 | 91.5 | 56.7
Gas [Member] | WPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 174.9 | 151.4 | 163.9
Depreciation and amortization |  |  |  |  |  |  |  |  | 16.0 | 14.9 | 13.6
Operating income (loss) |  |  |  |  |  |  |  |  | 24.5 | 15.2 | 16.9
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | 0.0 | 0.0 | 0.0
Total assets | 471.9 |  |  |  | 437.8 |  |  |  | 471.9 | 437.8 | 391.1
Investments in equity method subsidiaries | 0.0 |  |  |  | 0.0 |  |  |  | 0.0 | 0.0 | 0.0
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 44.5 | 45.6 | 49.7
Other Utility [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 47.5 | 48.6 | 57.9
Depreciation and amortization |  |  |  |  |  |  |  |  | 7.7 | 2.1 | 1.8
Operating income (loss) |  |  |  |  |  |  |  |  | (11.7) | (4.8) | 1.9
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | 0.0 | 0.0 | 0.0
Total assets | 766.5 |  |  |  | 781.0 |  |  |  | 766.5 | 781.0 | 828.9
Investments in equity method subsidiaries | 0.0 |  |  |  | 0.0 |  |  |  | 0.0 | 0.0 | 0.0
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 1.7 | 0.1 | 1.4
Other Utility [Member] | IPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 45.4 | 46.7 | 53.4
Depreciation and amortization |  |  |  |  |  |  |  |  | 7.7 | 2.1 | 1.8
Operating income (loss) |  |  |  |  |  |  |  |  | (5.0) | 3.3 | 5.4
Total assets | 353.7 |  |  |  | 373.2 |  |  |  | 353.7 | 373.2 | 406.8
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 1.2 | 0.1 | 1.4
Other Utility [Member] | WPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 2.1 | 1.9 | 4.5
Depreciation and amortization |  |  |  |  |  |  |  |  | 0.0 | 0.0 | 0.0
Operating income (loss) |  |  |  |  |  |  |  |  | (6.7) | (8.1) | (3.5)
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | 0.0 | (39.1) | (34.2)
Total assets | 412.8 |  |  |  | 407.8 |  |  |  | 412.8 | 407.8 | 715.4
Investments in equity method subsidiaries | 0.0 |  |  |  | 0.0 |  |  |  | 0.0 | 0.0 | 293.3
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 0.5 | 11.5 | 3.3
Utility Business [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 3,343.1 | 3,279.5 | 3,209.6
Depreciation and amortization |  |  |  |  |  |  |  |  | 457.9 | 403.3 | 391.5
Operating income (loss) |  |  |  |  |  |  |  |  | 620.1 | 597.8 | 550.6
Interest expense |  |  |  |  |  |  |  |  | 206.2 | 194.6 | 189.2
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | (0.7) | (0.7) | (0.9)
Income tax expense (benefit) |  |  |  |  |  |  |  |  | 51.0 | 71.4 | 46.2
Net income (loss) attributable to common shareowners |  |  |  |  |  |  |  |  | 403.4 | 385.2 | 343.4
Total assets | 13,362.5 |  |  |  | 12,595.0 |  |  |  | 13,362.5 | 12,595.0 | 11,686.2
Investments in equity method subsidiaries | 8.3 |  |  |  | 7.7 |  |  |  | 8.3 | 7.7 | 8.7
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 1,281.8 | 1,131.2 | 960.3
Utility Business [Member] | IPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 1,870.3 | 1,820.4 | 1,774.5
Depreciation and amortization |  |  |  |  |  |  |  |  | 245.0 | 210.8 | 207.2
Operating income (loss) |  |  |  |  |  |  |  |  | 296.9 | 270.8 | 241.9
Interest expense |  |  |  |  |  |  |  |  | 112.4 | 103.2 | 96.8
Income tax expense (benefit) |  |  |  |  |  |  |  |  | (10.9) | (5.9) | (22.7)
Net income (loss) attributable to common shareowners |  |  |  |  |  |  |  |  | 216.8 | 215.6 | 186.0
Total assets | 7,606.0 |  |  |  | 7,304.7 |  |  |  | 7,606.0 | 7,304.7 | 6,709.1
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 676.0 | 689.7 | 619.3
Utility Business [Member] | WPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 1,472.8 | 1,459.1 | 1,435.1
Depreciation and amortization |  |  |  |  |  |  |  |  | 212.9 | 192.5 | 184.3
Operating income (loss) |  |  |  |  |  |  |  |  | 323.2 | 327.0 | 308.7
Interest expense |  |  |  |  |  |  |  |  | 93.8 | 91.4 | 92.4
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | (0.7) | (39.8) | (35.1)
Income tax expense (benefit) |  |  |  |  |  |  |  |  | 61.9 | 93.3 | 82.9
Net income (loss) attributable to common shareowners |  |  |  |  |  |  |  |  | 186.6 | 190.4 | 176.3
Total assets | 5,756.5 |  |  |  | 5,290.3 |  |  |  | 5,756.5 | 5,290.3 | 5,270.4
Investments in equity method subsidiaries | 8.3 |  |  |  | 7.7 |  |  |  | 8.3 | 7.7 | 302.0
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 637.4 | 453.0 | 344.3
Non-Utility [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 39.1 | 40.5 | 44.0
Depreciation and amortization |  |  |  |  |  |  |  |  | 3.9 | 8.3 | 9.8
Operating income (loss) |  |  |  |  |  |  |  |  | 33.3 | (60.8) | 26.4
Interest expense |  |  |  |  |  |  |  |  | 9.4 | 1.6 |
Interest income |  |  |  |  |  |  |  |  |  |  | (2.1)
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | (44.1) | (38.9) | (32.9)
Income tax expense (benefit) |  |  |  |  |  |  |  |  | 15.7 | (12.0) | 24.2
Net income (loss) attributable to common shareowners |  |  |  |  |  |  |  |  | 53.9 | (13.7) | 34.8
Total assets | 825.3 |  |  |  | 778.8 |  |  |  | 825.3 | 778.8 | 809.0
Investments in equity method subsidiaries | $ 373.1 |  |  |  | $ 318.3 |  |  |  | 373.1 | 318.3 | 294.2
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | $ 185.1 | $ 65.6 | $ 74.0

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