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Segments Of Business (Schedule Of Segment Of Business) (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues | $ 873.5 | $ 928.6 | $ 816.1 | $ 916.3 | $ 856.1 | $ 906.9 | $ 765.3 | $ 853.9 | $ 3,534.5 | $ 3,382.2 | $ 3,320.0
Depreciation and amortization |  |  |  |  |  |  |  |  | 506.9 | 461.8 | 411.6
Operating income (loss) | 121.4 | 256.1 | 151.2 | 165.7 | 134.0 | 236.3 | 153.7 | 147.2 | 694.4 | 671.2 | 554.1
Interest expense |  |  |  |  |  |  |  |  | 247.0 | 215.6 | 196.2
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | (54.6) | (44.8) | (39.6)
Income tax expense (benefit) |  |  |  |  |  |  |  |  | 47.7 | 66.7 | 59.4
Net income (loss) attributable to common shareowners | 85.3 | 205.5 | 100.4 | 120.9 | 93.8 | 168.8 | 94.3 | 100.4 | 512.1 | 457.3 | 371.5
Total assets | 15,426.0 |  |  |  | 14,187.8 |  |  |  | 15,426.0 | 14,187.8 | 13,373.8
Investments in equity method subsidiaries | 421.3 |  |  |  | 381.4 |  |  |  | 421.3 | 381.4 | 326.0
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 1,633.9 | 1,466.9 | 1,196.8
IPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues | 494.1 | 547.6 | 474.8 | 525.8 | 472.2 | 527.4 | 420.2 | 450.5 | 2,042.3 | 1,870.3 | 1,820.4
Depreciation and amortization |  |  |  |  |  |  |  |  | 283.5 | 245.0 | 210.8
Operating income (loss) | 54.4 | 143.1 | 77.7 | 75.6 | 50.9 | 133.8 | 68.1 | 51.3 | 350.8 | 304.1 | 277.6
Interest expense |  |  |  |  |  |  |  |  | 119.4 | 112.4 | 103.2
Income tax expense (benefit) |  |  |  |  |  |  |  |  | (3.2) | (10.9) | (5.9)
Net income (loss) attributable to common shareowners | 39.1 | 126.5 | 51.7 | 46.7 | 16.4 | 120.4 | 42.8 | 37.2 | 264.0 | 216.8 | 215.6
Total assets | 8,411.4 |  |  |  | 7,606.0 |  |  |  | 8,411.4 | 7,606.0 |
WPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues | 369.4 | 370.7 | 330.8 | 381.7 | 374.7 | 370.2 | 334.8 | 393.1 | 1,452.6 | 1,472.8 | 1,459.1
Depreciation and amortization |  |  |  |  |  |  |  |  | 219.4 | 212.9 | 192.5
Operating income (loss) | 61.3 | 104.2 | 63.4 | 84.0 | 75.4 | 93.5 | 76.2 | 88.6 | 312.9 | 333.7 | 337.2
Interest expense |  |  |  |  |  |  |  |  | 97.8 | 93.8 | 91.4
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | (0.9) | (0.7) | (39.8)
Income tax expense (benefit) |  |  |  |  |  |  |  |  | 36.2 | 61.9 | 93.3
Net income (loss) attributable to common shareowners | 38.0 | $ 76.3 | $ 39.8 | $ 54.0 | 53.2 | $ 49.8 | $ 38.1 | $ 45.5 | 208.1 | 186.6 | 190.4
Total assets | 6,152.5 |  |  |  | 5,756.5 |  |  |  | 6,152.5 | 5,756.5 |
Electric [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 3,000.3 | 2,894.7 | 2,875.5
Depreciation and amortization |  |  |  |  |  |  |  |  | 457.3 | 412.0 | 367.0
Operating income (loss) |  |  |  |  |  |  |  |  | 610.2 | 601.7 | 586.5
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | (0.9) | (0.7) | (0.7)
Total assets | 12,486.3 |  |  |  | 11,396.2 |  |  |  | 12,486.3 | 11,396.2 | 10,722.9
Investments in equity method subsidiaries | 8.1 |  |  |  | 8.3 |  |  |  | 8.1 | 8.3 | 7.7
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 1,421.1 | 1,154.9 | 994.0
Electric [Member] | IPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 1,731.1 | 1,598.9 | 1,569.7
Depreciation and amortization |  |  |  |  |  |  |  |  | 254.7 | 215.1 | 189.4
Operating income (loss) |  |  |  |  |  |  |  |  | 318.2 | 287.3 | 257.8
Total assets | 7,219.9 |  |  |  | 6,524.4 |  |  |  | 7,219.9 | 6,524.4 | 6,278.2
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 890.6 | 594.1 | 598.1
Electric [Member] | WPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 1,269.2 | 1,295.8 | 1,305.8
Depreciation and amortization |  |  |  |  |  |  |  |  | 202.6 | 196.9 | 177.6
Operating income (loss) |  |  |  |  |  |  |  |  | 292.0 | 314.4 | 328.7
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  |  |  | (0.7)
Total assets | 5,266.4 |  |  |  | 4,871.8 |  |  |  | 5,266.4 | 4,871.8 | 4,444.7
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 530.5 | 592.4 | 395.9
Gas [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 446.6 | 400.9 | 355.4
Depreciation and amortization |  |  |  |  |  |  |  |  | 42.0 | 38.2 | 34.2
Operating income (loss) |  |  |  |  |  |  |  |  | 53.2 | 47.7 | 33.0
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | 0.0 | 0.0 | 0.0
Total assets | 1,184.4 |  |  |  | 1,199.8 |  |  |  | 1,184.4 | 1,199.8 | 1,091.1
Investments in equity method subsidiaries | 0.0 |  |  |  | 0.0 |  |  |  | 0.0 | 0.0 | 0.0
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 146.8 | 125.2 | 137.1
Gas [Member] | IPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 266.2 | 226.0 | 204.0
Depreciation and amortization |  |  |  |  |  |  |  |  | 25.2 | 22.2 | 19.3
Operating income (loss) |  |  |  |  |  |  |  |  | 28.3 | 21.7 | 16.4
Total assets | 687.5 |  |  |  | 727.9 |  |  |  | 687.5 | 727.9 | 653.3
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 99.7 | 80.7 | 91.5
Gas [Member] | WPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 180.4 | 174.9 | 151.4
Depreciation and amortization |  |  |  |  |  |  |  |  | 16.8 | 16.0 | 14.9
Operating income (loss) |  |  |  |  |  |  |  |  | 24.9 | 26.0 | 16.6
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  |  |  | 0.0
Total assets | 496.9 |  |  |  | 471.9 |  |  |  | 496.9 | 471.9 | 437.8
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 47.1 | 44.5 | 45.6
Other Utility [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 48.0 | 47.5 | 48.6
Depreciation and amortization |  |  |  |  |  |  |  |  | 3.6 | 7.7 | 2.1
Operating income (loss) |  |  |  |  |  |  |  |  | 0.3 | (11.6) | (4.7)
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | 0.0 | 0.0 | 0.0
Total assets | 893.2 |  |  |  | 766.5 |  |  |  | 893.2 | 766.5 | 781.0
Investments in equity method subsidiaries | 0.0 |  |  |  | 0.0 |  |  |  | 0.0 | 0.0 | 0.0
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 0.4 | 1.7 | 0.1
Other Utility [Member] | IPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 45.0 | 45.4 | 46.7
Depreciation and amortization |  |  |  |  |  |  |  |  | 3.6 | 7.7 | 2.1
Operating income (loss) |  |  |  |  |  |  |  |  | 4.3 | (4.9) | 3.4
Total assets | 504.0 |  |  |  | 353.7 |  |  |  | 504.0 | 353.7 | 373.2
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 0.4 | 1.2 | 0.1
Other Utility [Member] | WPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 3.0 | 2.1 | 1.9
Depreciation and amortization |  |  |  |  |  |  |  |  | 0.0 | 0.0 | 0.0
Operating income (loss) |  |  |  |  |  |  |  |  | (4.0) | (6.7) | (8.1)
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  |  |  | (39.1)
Total assets | 389.2 |  |  |  | 412.8 |  |  |  | 389.2 | 412.8 | 407.8
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 0.0 | 0.5 | 11.5
Utility Business [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 3,494.9 | 3,343.1 | 3,279.5
Depreciation and amortization |  |  |  |  |  |  |  |  | 502.9 | 457.9 | 403.3
Operating income (loss) |  |  |  |  |  |  |  |  | 663.7 | 637.8 | 614.8
Interest expense |  |  |  |  |  |  |  |  | 217.2 | 206.2 | 194.6
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | (0.9) | (0.7) | (0.7)
Income tax expense (benefit) |  |  |  |  |  |  |  |  | 33.0 | 51.0 | 71.4
Net income (loss) attributable to common shareowners |  |  |  |  |  |  |  |  | 472.1 | 403.4 | 385.2
Total assets | 14,563.9 |  |  |  | 13,362.5 |  |  |  | 14,563.9 | 13,362.5 | 12,595.0
Investments in equity method subsidiaries | 8.1 |  |  |  | 8.3 |  |  |  | 8.1 | 8.3 | 7.7
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 1,568.3 | 1,281.8 | 1,131.2
Utility Business [Member] | IPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 2,042.3 | 1,870.3 | 1,820.4
Depreciation and amortization |  |  |  |  |  |  |  |  | 283.5 | 245.0 | 210.8
Operating income (loss) |  |  |  |  |  |  |  |  | 350.8 | 304.1 | 277.6
Interest expense |  |  |  |  |  |  |  |  | 119.4 | 112.4 | 103.2
Income tax expense (benefit) |  |  |  |  |  |  |  |  | (3.2) | (10.9) | (5.9)
Net income (loss) attributable to common shareowners |  |  |  |  |  |  |  |  | 264.0 | 216.8 | 215.6
Total assets | 8,411.4 |  |  |  | 7,606.0 |  |  |  | 8,411.4 | 7,606.0 | 7,304.7
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 990.7 | 676.0 | 689.7
Utility Business [Member] | WPL [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 1,452.6 | 1,472.8 | 1,459.1
Depreciation and amortization |  |  |  |  |  |  |  |  | 219.4 | 212.9 | 192.5
Operating income (loss) |  |  |  |  |  |  |  |  | 312.9 | 333.7 | 337.2
Interest expense |  |  |  |  |  |  |  |  | 97.8 | 93.8 | 91.4
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  |  |  | (39.8)
Income tax expense (benefit) |  |  |  |  |  |  |  |  | 36.2 | 61.9 | 93.3
Net income (loss) attributable to common shareowners |  |  |  |  |  |  |  |  | 208.1 | 186.6 | 190.4
Total assets | 6,152.5 |  |  |  | 5,756.5 |  |  |  | 6,152.5 | 5,756.5 | 5,290.3
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | 577.6 | 637.4 | 453.0
Non-Utility [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 39.6 | 39.1 | 40.5
Depreciation and amortization |  |  |  |  |  |  |  |  | 4.0 | 3.9 | 8.3
Operating income (loss) |  |  |  |  |  |  |  |  | 30.7 | 33.4 | (60.7)
Interest expense |  |  |  |  |  |  |  |  | 29.8 | 9.4 | 1.6
Equity (income) loss from unconsolidated investments, net |  |  |  |  |  |  |  |  | (53.7) | (44.1) | (38.9)
Income tax expense (benefit) |  |  |  |  |  |  |  |  | 14.7 | 15.7 | (12.0)
Net income (loss) attributable to common shareowners |  |  |  |  |  |  |  |  | 40.0 | 53.9 | (13.7)
Total assets | 862.1 |  |  |  | 825.3 |  |  |  | 862.1 | 825.3 | 778.8
Investments in equity method subsidiaries | $ 413.2 |  |  |  | $ 373.1 |  |  |  | 413.2 | 373.1 | 318.3
Construction and acquisition expenditures |  |  |  |  |  |  |  |  | $ 65.6 | $ 185.1 | $ 65.6

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