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Segments Of Business (Tables) | 12 Months Ended
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Dec. 31, 2016
Segment Reporting Information [Line Items] |
Schedule of Segments of Business | Certain financial information relating to Alliant Energy’s business segments, which represent the services provided to its customers, was as follows (in millions):
| Utility |  | Non-Regulated, |  | Alliant Energy
2016 | Electric |  | Gas |  | Other |  | Total |  | Parent and Other |  | Consolidated
Operating revenues |  | $2,875.5 |  |  |  | $355.4 |  |  |  | $48.6 |  |  |  | $3,279.5 |  |  |  | $40.5 |  |  |  | $3,320.0 |
Depreciation and amortization | 367.0 |  |  | 34.2 |  |  | 2.1 |  |  | 403.3 |  |  | 8.3 |  |  | 411.6 |
Operating income (loss) | 571.9 |  |  | 30.7 |  |  | (4.8 | ) |  | 597.8 |  |  | (60.8 | ) |  | 537.0 |
Interest expense |  |  |  |  |  |  | 194.6 |  |  | 1.6 |  |  | 196.2 |
Equity (income) loss from unconsolidated investments, net | (39.8 | ) |  | — |  |  | — |  |  | (39.8 | ) |  | 0.2 |  |  | (39.6 | )
Income tax expense (benefit) |  |  |  |  |  |  | 87.4 |  |  | (28.0 | ) |  | 59.4 |
Net income (loss) attributable to Alliant Energy common shareowners |  |  |  |  |  |  | 406.0 |  |  | (34.5 | ) |  | 371.5 |
Total assets | 11,040.5 |  |  | 1,091.1 |  |  | 781.0 |  |  | 12,912.6 |  |  | 461.2 |  |  | 13,373.8 |
Investments in equity method subsidiaries | 325.3 |  |  | — |  |  | — |  |  | 325.3 |  |  | 0.7 |  |  | 326.0 |
Construction and acquisition expenditures | 1,005.5 |  |  | 137.1 |  |  | 0.1 |  |  | 1,142.7 |  |  | 54.1 |  |  | 1,196.8 |
| Utility |  | Non-Regulated, |  | Alliant Energy
2015 | Electric |  | Gas |  | Other |  | Total |  | Parent and Other |  | Consolidated
Operating revenues |  | $2,770.5 |  |  |  | $381.2 |  |  |  | $57.9 |  |  |  | $3,209.6 |  |  |  | $44.0 |  |  |  | $3,253.6 |
Depreciation and amortization | 358.6 |  |  | 31.1 |  |  | 1.8 |  |  | 391.5 |  |  | 9.8 |  |  | 401.3 |
Operating income | 514.1 |  |  | 34.6 |  |  | 1.9 |  |  | 550.6 |  |  | 26.4 |  |  | 577.0 |
Interest expense |  |  |  |  |  |  | 189.2 |  |  | (2.1 | ) |  | 187.1 |
Equity (income) loss from unconsolidated investments, net | (35.1 | ) |  | — |  |  | — |  |  | (35.1 | ) |  | 1.3 |  |  | (33.8 | )
Income taxes |  |  |  |  |  |  | 60.2 |  |  | 10.2 |  |  | 70.4 |
Net income attributable to Alliant Energy common shareowners |  |  |  |  |  |  | 362.3 |  |  | 15.9 |  |  | 378.2 |
Total assets | 10,211.3 |  |  | 939.3 |  |  | 828.9 |  |  | 11,979.5 |  |  | 515.7 |  |  | 12,495.2 |
Investments in equity method subsidiaries | 302.0 |  |  | — |  |  | — |  |  | 302.0 |  |  | 0.9 |  |  | 302.9 |
Construction and acquisition expenditures | 855.8 |  |  | 106.4 |  |  | 1.4 |  |  | 963.6 |  |  | 70.7 |  |  | 1,034.3 |
| Utility |  | Non-Regulated, |  | Alliant Energy
2014 | Electric |  | Gas |  | Other |  | Total |  | Parent and Other |  | Consolidated
Operating revenues |  | $2,713.6 |  |  |  | $517.5 |  |  |  | $66.1 |  |  |  | $3,297.2 |  |  |  | $53.1 |  |  |  | $3,350.3 |
Depreciation and amortization | 347.0 |  |  | 29.9 |  |  | 1.8 |  |  | 378.7 |  |  | 9.4 |  |  | 388.1 |
Operating income | 442.4 |  |  | 53.8 |  |  | 14.0 |  |  | 510.2 |  |  | 33.4 |  |  | 543.6 |
Interest expense |  |  |  |  |  |  | 176.3 |  |  | 4.3 |  |  | 180.6 |
Equity income (loss) from unconsolidated investments, net | (42.8 | ) |  | — |  |  | — |  |  | (42.8 | ) |  | 2.4 |  |  | (40.4 | )
Income taxes |  |  |  |  |  |  | 36.4 |  |  | 7.9 |  |  | 44.3 |
Net income attributable to Alliant Energy common shareowners |  |  |  |  |  |  | 362.0 |  |  | 21.1 |  |  | 383.1 |
Total assets | 9,660.4 |  |  | 913.5 |  |  | 993.9 |  |  | 11,567.8 |  |  | 495.7 |  |  | 12,063.5 |
Investments in equity method subsidiaries | 294.3 |  |  | — |  |  | — |  |  | 294.3 |  |  | 2.3 |  |  | 296.6 |
Construction and acquisition expenditures | 774.8 |  |  | 63.2 |  |  | 0.9 |  |  | 838.9 |  |  | 63.9 |  |  | 902.8 |
IPL [Member] |
Segment Reporting Information [Line Items] |
Schedule of Segments of Business | Certain financial information relating to IPL’s business segments, which represent the services provided to its customers, was as follows (in millions):
2016 | Electric |  | Gas |  | Other |  | Total
Operating revenues |  | $1,569.7 |  |  |  | $204.0 |  |  |  | $46.7 |  |  |  | $1,820.4 |
Depreciation and amortization | 189.4 |  |  | 19.3 |  |  | 2.1 |  |  | 210.8 |
Operating income | 252.0 |  |  | 15.5 |  |  | 3.3 |  |  | 270.8 |
Interest expense |  |  |  |  |  |  | 103.2 |
Income tax benefit |  |  |  |  |  |  | (5.9 | )
Earnings available for common stock |  |  |  |  |  |  | 215.6 |
Total assets | 6,278.2 |  |  | 653.3 |  |  | 373.2 |  |  | 7,304.7 |
Construction and acquisition expenditures | 598.1 |  |  | 91.5 |  |  | 0.1 |  |  | 689.7 |
2015 | Electric |  | Gas |  | Other |  | Total
Operating revenues |  | $1,503.8 |  |  |  | $217.3 |  |  |  | $53.4 |  |  |  | $1,774.5 |
Depreciation and amortization | 187.9 |  |  | 17.5 |  |  | 1.8 |  |  | 207.2 |
Operating income | 218.8 |  |  | 17.7 |  |  | 5.4 |  |  | 241.9 |
Interest expense |  |  |  |  |  |  | 96.8 |
Income tax benefit |  |  |  |  |  |  | (22.7 | )
Earnings available for common stock |  |  |  |  |  |  | 186.0 |
Total assets | 5,754.1 |  |  | 548.2 |  |  | 406.8 |  |  | 6,709.1 |
Construction and acquisition expenditures | 561.2 |  |  | 56.7 |  |  | 1.4 |  |  | 619.3 |
2014 | Electric |  | Gas |  | Other |  | Total
Operating revenues |  | $1,493.3 |  |  |  | $296.5 |  |  |  | $58.3 |  |  |  | $1,848.1 |
Depreciation and amortization | 178.7 |  |  | 17.0 |  |  | 1.8 |  |  | 197.5 |
Operating income | 166.8 |  |  | 25.7 |  |  | 16.7 |  |  | 209.2 |
Interest expense |  |  |  |  |  |  | 89.9 |
Income tax benefit |  |  |  |  |  |  | (48.9 | )
Earnings available for common stock |  |  |  |  |  |  | 181.6 |
Total assets | 5,398.3 |  |  | 544.1 |  |  | 507.8 |  |  | 6,450.2 |
Construction and acquisition expenditures | 490.0 |  |  | 35.1 |  |  | 0.9 |  |  | 526.0 |
WPL [Member] |
Segment Reporting Information [Line Items] |
Schedule of Segments of Business | Certain financial information relating to WPL’s business segments, which represent the services provided to its customers, was as follows (in millions):
2016 | Electric |  | Gas |  | Other |  | Total
Operating revenues |  | $1,305.8 |  |  |  | $151.4 |  |  |  | $1.9 |  |  |  | $1,459.1 |
Depreciation and amortization | 177.6 |  |  | 14.9 |  |  | — |  |  | 192.5 |
Operating income (loss) | 319.9 |  |  | 15.2 |  |  | (8.1 | ) |  | 327.0 |
Interest expense |  |  |  |  |  |  | 91.4 |
Equity income from unconsolidated investments | (39.8 | ) |  | — |  |  | — |  |  | (39.8 | )
Income taxes |  |  |  |  |  |  | 93.3 |
Earnings available for common stock |  |  |  |  |  |  | 190.4 |
Total assets | 4,444.7 |  |  | 437.8 |  |  | 407.8 |  |  | 5,290.3 |
Investments in equity method subsidiaries | 7.7 |  |  | — |  |  | — |  |  | 7.7 |
Construction and acquisition expenditures | 407.4 |  |  | 45.6 |  |  | — |  |  | 453.0 |
2015 | Electric |  | Gas |  | Other |  | Total
Operating revenues |  | $1,266.7 |  |  |  | $163.9 |  |  |  | $4.5 |  |  |  | $1,435.1 |
Depreciation and amortization | 170.7 |  |  | 13.6 |  |  | — |  |  | 184.3 |
Operating income (loss) | 295.3 |  |  | 16.9 |  |  | (3.5 | ) |  | 308.7 |
Interest expense |  |  |  |  |  |  | 92.4 |
Equity income from unconsolidated investments | (35.1 | ) |  | — |  |  | — |  |  | (35.1 | )
Income taxes |  |  |  |  |  |  | 82.9 |
Earnings available for common stock |  |  |  |  |  |  | 176.3 |
Total assets | 4,457.2 |  |  | 391.1 |  |  | 422.1 |  |  | 5,270.4 |
Investments in equity method subsidiaries | 302.0 |  |  | — |  |  | — |  |  | 302.0 |
Construction and acquisition expenditures | 294.6 |  |  | 49.7 |  |  | — |  |  | 344.3 |
2014 | Electric |  | Gas |  | Other |  | Total
Operating revenues |  | $1,220.3 |  |  |  | $221.0 |  |  |  | $7.8 |  |  |  | $1,449.1 |
Depreciation and amortization | 168.3 |  |  | 12.9 |  |  | — |  |  | 181.2 |
Operating income (loss) | 275.6 |  |  | 28.1 |  |  | (2.7 | ) |  | 301.0 |
Interest expense |  |  |  |  |  |  | 86.4 |
Equity income from unconsolidated investments | (42.8 | ) |  | — |  |  | — |  |  | (42.8 | )
Income taxes |  |  |  |  |  |  | 85.3 |
Earnings available for common stock |  |  |  |  |  |  | 180.4 |
Total assets | 4,262.1 |  |  | 369.4 |  |  | 486.1 |  |  | 5,117.6 |
Investments in equity method subsidiaries | 294.3 |  |  | — |  |  | — |  |  | 294.3 |
Construction and acquisition expenditures | 284.8 |  |  | 28.1 |  |  | — |  |  | 312.9 |

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