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Summary Of Significant Accounting Policies Summary Of Significant Accounting Policies (Schedule Of New Accounting Standards And Changes In Accounting Principles) (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 | Dec. 31, 2012
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Deferred tax assets | $ 0.0 |  |  |  | $ 150.1 |  |  |  | $ 0.0 | $ 150.1 |  |
Total current assets | 826.8 |  |  |  | 1,043.1 |  |  |  | 826.8 | 1,043.1 |  |
Deferred charges and other | 14.6 |  |  |  | 21.5 |  |  |  | 14.6 | 21.5 |  |
Total other assets | 1,803.0 |  |  |  | 1,737.1 |  |  |  | 1,803.0 | 1,737.1 |  |
Total assets | 12,495.2 |  |  |  | 12,063.5 |  |  |  | 12,495.2 | 12,063.5 | $ 11,092.5 |
Other current liabilities | 296.6 |  |  |  | 262.4 |  |  |  | 296.6 | 262.4 |  |
Total current liabilities | 1,359.3 |  |  |  | 1,214.7 |  |  |  | 1,359.3 | 1,214.7 |  |
Long-term debt, net (excluding current portion) | 3,522.2 |  |  |  | 3,584.3 |  |  |  | 3,522.2 | 3,584.3 |  |
Deferred tax liabilities | 2,381.2 |  |  |  | 2,321.1 |  |  |  | 2,381.2 | 2,321.1 |  |
Total other liabilities | 3,689.6 |  |  |  | 3,624.0 |  |  |  | 3,689.6 | 3,624.0 |  |
Retained earnings | 2,068.9 |  |  |  | 1,938.0 |  |  |  | 2,068.9 | 1,938.0 |  |
Total common equity | 3,724.1 |  |  |  | 3,438.7 |  |  |  | 3,724.1 | 3,438.7 | 3,281.4 | $ 3,134.9
Total equity | 3,924.1 |  |  |  | 3,640.5 |  |  |  | 3,924.1 | 3,640.5 |  |
Total liabilities and equity | 12,495.2 |  |  |  | 12,063.5 |  |  |  | 12,495.2 | 12,063.5 |  |
Income tax expense (benefit) |  |  |  |  |  |  |  |  | 70.4 | 44.3 | 53.9 |
Net income |  |  |  |  |  |  |  |  | 388.4 | 393.3 | 376.2 |
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 |
Deferred tax expense (benefit) and investment tax credits |  |  |  |  |  |  |  |  | 114.2 | 55.2 | 108.3 |
Other |  |  |  |  |  |  |  |  | (5.4) | 59.7 | 23.7 |
Scenario, Previously Reported [Member] |  |  |  |  |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Deferred charges and other |  |  |  |  | 43.9 |  |  |  |  | 43.9 |  |
Total other assets |  |  |  |  | 1,759.5 |  |  |  |  | 1,759.5 |  |
Total assets |  |  |  |  | 12,085.9 |  |  |  |  | 12,085.9 |  |
Long-term debt, net (excluding current portion) |  |  |  |  | 3,606.7 |  |  |  |  | 3,606.7 |  |
Total liabilities and equity |  |  |  |  | 12,085.9 |  |  |  |  | 12,085.9 |  |
New Accounting Pronouncement, Early Adoption, Effect [Member] |  |  |  |  |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Deferred charges and other |  |  |  |  | (22.4) |  |  |  |  | (22.4) |  |
Total other assets |  |  |  |  | (22.4) |  |  |  |  | (22.4) |  |
Total assets |  |  |  |  | (22.4) |  |  |  |  | (22.4) |  |
Long-term debt, net (excluding current portion) |  |  |  |  | (22.4) |  |  |  |  | (22.4) |  |
Total liabilities and equity |  |  |  |  | (22.4) |  |  |  |  | (22.4) |  |
IPL [Member] |  |  |  |  |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Deferred tax assets | 0.0 |  |  |  | 104.0 |  |  |  | 0.0 | 104.0 |  |
Total current assets | 396.4 |  |  |  | 555.2 |  |  |  | 396.4 | 555.2 |  |
Deferred charges and other | 5.0 |  |  |  | 2.0 |  |  |  | 5.0 | 2.0 |  |
Total other assets | 1,368.0 |  |  |  | 1,321.2 |  |  |  | 1,368.0 | 1,321.2 |  |
Total assets | 6,709.1 |  |  |  | 6,450.2 |  |  |  | 6,709.1 | 6,450.2 |  |
Other current liabilities | 69.5 |  |  |  | 64.6 |  |  |  | 69.5 | 64.6 |  |
Total current liabilities | 531.1 |  |  |  | 705.9 |  |  |  | 531.1 | 705.9 |  |
Long-term debt, net (excluding current portion) | 1,856.9 |  |  |  | 1,608.0 |  |  |  | 1,856.9 | 1,608.0 |  |
Deferred tax liabilities | 1,378.0 |  |  |  | 1,370.3 |  |  |  | 1,378.0 | 1,370.3 |  |
Total other liabilities | 2,125.8 |  |  |  | 2,152.0 |  |  |  | 2,125.8 | 2,152.0 |  |
Retained earnings | 554.1 |  |  |  | 508.1 |  |  |  | 554.1 | 508.1 | 461.9 | 415.2
Total common equity | 1,995.3 |  |  |  | 1,784.3 |  |  |  | 1,995.3 | 1,784.3 | 1,648.1 | 1,486.4
Total equity | 2,195.3 |  |  |  | 1,984.3 |  |  |  | 2,195.3 | 1,984.3 |  |
Total liabilities and equity | 6,709.1 |  |  |  | 6,450.2 |  |  |  | 6,709.1 | 6,450.2 |  |
Income tax expense (benefit) |  |  |  |  |  |  |  |  | (22.7) | (48.9) | (36.3) |
Net income | 8.0 | 119.1 | 19.0 | 50.1 | 21.4 | 104.6 | 20.5 | 45.3 | 196.2 | 191.8 | 188.3 |
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 |
Deferred tax expense (benefit) and investment tax credits |  |  |  |  |  |  |  |  | 28.9 | (11.5) | 3.0 |
Other |  |  |  |  |  |  |  |  | 43.0 | 36.6 | (11.2) |
IPL [Member] | Scenario, Previously Reported [Member] |  |  |  |  |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Deferred tax assets |  |  |  |  | 104.9 |  |  |  |  | 104.9 |  |
Total current assets |  |  |  |  | 556.1 |  |  |  |  | 556.1 |  |
Deferred charges and other |  |  |  |  | 12.7 |  |  |  |  | 12.7 |  |
Total other assets |  |  |  |  | 1,331.9 |  |  |  |  | 1,331.9 |  |
Total assets |  |  |  |  | 6,461.8 |  |  |  |  | 6,461.8 |  |
Long-term debt, net (excluding current portion) |  |  |  |  | 1,618.7 |  |  |  |  | 1,618.7 |  |
Deferred tax liabilities | 1,346.7 |  |  |  | 1,341.4 |  |  |  | 1,346.7 | 1,341.4 |  |
Total other liabilities | 2,094.5 |  |  |  | 2,123.1 |  |  |  | 2,094.5 | 2,123.1 |  |
Retained earnings | 585.4 |  |  |  | 537.9 |  |  |  | 585.4 | 537.9 | 493.5 | 448.0
Total common equity | 2,026.6 |  |  |  | 1,814.1 |  |  |  | 2,026.6 | 1,814.1 |  |
Total equity | 2,226.6 |  |  |  | 2,014.1 |  |  |  | 2,226.6 | 2,014.1 |  |
Total liabilities and equity |  |  |  |  | 6,461.8 |  |  |  |  | 6,461.8 |  |
Income tax expense (benefit) |  |  |  |  |  |  |  |  |  | (51.7) | (37.9) |
Net income |  | 120.0 | 19.2 | 50.4 | 22.6 | 105.1 | 20.9 | 46.0 |  | 194.6 | 189.9 |
Net income (loss) attributable to common shareowners |  | 117.4 | 16.7 | 47.8 | 20.1 | 102.5 | 18.4 | 43.4 |  | 184.4 | 173.6 |
Deferred tax expense (benefit) and investment tax credits |  |  |  |  |  |  |  |  |  | (9.7) | 4.2 |
Other |  |  |  |  |  |  |  |  |  | 32.0 | (14.0) |
IPL [Member] | Restatement Adjustment [Member] |  |  |  |  |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Deferred tax assets |  |  |  |  | (0.9) |  |  |  |  | (0.9) |  |
Total current assets |  |  |  |  | (0.9) |  |  |  |  | (0.9) |  |
Total assets |  |  |  |  | (0.9) |  |  |  |  | (0.9) |  |
Deferred tax liabilities | 31.3 |  |  |  | 28.9 |  |  |  | 31.3 | 28.9 |  |
Total other liabilities | 31.3 |  |  |  | 28.9 |  |  |  | 31.3 | 28.9 |  |
Retained earnings | (31.3) |  |  |  | (29.8) |  |  |  | (31.3) | (29.8) | (31.6) | (32.8)
Total common equity | (31.3) |  |  |  | (29.8) |  |  |  | (31.3) | (29.8) |  |
Total equity | (31.3) |  |  |  | (29.8) |  |  |  | (31.3) | (29.8) |  |
Total liabilities and equity |  |  |  |  | (0.9) |  |  |  |  | (0.9) |  |
Income tax expense (benefit) |  |  |  |  |  |  |  |  |  | 2.8 | 1.6 |
Net income |  |  |  |  |  |  |  |  |  | (2.8) | (1.6) |
Net income (loss) attributable to common shareowners |  |  |  |  |  |  |  |  |  | (2.8) | (1.6) |
Deferred tax expense (benefit) and investment tax credits |  |  |  |  |  |  |  |  |  | (1.8) | (1.2) |
Other |  |  |  |  |  |  |  |  |  | 4.6 | 2.8 |
IPL [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member] |  |  |  |  |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Deferred charges and other |  |  |  |  | (10.7) |  |  |  |  | (10.7) |  |
Total other assets |  |  |  |  | (10.7) |  |  |  |  | (10.7) |  |
Total assets |  |  |  |  | (10.7) |  |  |  |  | (10.7) |  |
Long-term debt, net (excluding current portion) |  |  |  |  | (10.7) |  |  |  |  | (10.7) |  |
Total liabilities and equity |  |  |  |  | (10.7) |  |  |  |  | (10.7) |  |
WPL [Member] |  |  |  |  |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Deferred tax assets | 0.0 |  |  |  | 37.7 |  |  |  | 0.0 | 37.7 |  |
Total current assets | 423.5 |  |  |  | 457.4 |  |  |  | 423.5 | 457.4 |  |
Deferred charges and other | 9.1 |  |  |  | 18.9 |  |  |  | 9.1 | 18.9 |  |
Total other assets | 434.5 |  |  |  | 415.3 |  |  |  | 434.5 | 415.3 |  |
Total assets | 5,270.4 |  |  |  | 5,117.6 |  |  |  | 5,270.4 | 5,117.6 |  |
Other current liabilities | 79.5 |  |  |  | 46.6 |  |  |  | 79.5 | 46.6 |  |
Total current liabilities | 336.9 |  |  |  | 310.3 |  |  |  | 336.9 | 310.3 |  |
Long-term debt, net (excluding current portion) | 1,533.9 |  |  |  | 1,532.5 |  |  |  | 1,533.9 | 1,532.5 |  |
Deferred tax liabilities | 1,005.4 |  |  |  | 967.1 |  |  |  | 1,005.4 | 967.1 |  |
Total other liabilities | 1,632.0 |  |  |  | 1,559.4 |  |  |  | 1,632.0 | 1,559.4 |  |
Retained earnings | 731.1 |  |  |  | 681.7 |  |  |  | 731.1 | 681.7 | 622.2 | 565.9
Total common equity | 1,756.3 |  |  |  | 1,706.9 |  |  |  | 1,756.3 | 1,706.9 |  |
Total equity | 1,767.6 |  |  |  | 1,715.4 |  |  |  | 1,767.6 | 1,715.4 | 1,647.4 | 1,591.3
Total liabilities and equity | 5,270.4 |  |  |  | 5,117.6 |  |  |  | 5,270.4 | 5,117.6 |  |
Income tax expense (benefit) |  |  |  |  |  |  |  |  | 82.9 | 85.3 | 85.6 |
Net income | 24.4 | 68.4 | 39.7 | 45.1 | 33.3 | 57.9 | 34.7 | 55.2 | 177.6 | 181.1 | 179.1 |
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 |
Deferred tax expense (benefit) and investment tax credits |  |  |  |  |  |  |  |  | 77.6 | 82.6 | 89.8 |
Other |  |  |  |  |  |  |  |  | 27.4 | (9.0) | (21.6) |
WPL [Member] | Scenario, Previously Reported [Member] |  |  |  |  |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Deferred tax assets |  |  |  |  | 37.5 |  |  |  |  | 37.5 |  |
Total current assets |  |  |  |  | 457.2 |  |  |  |  | 457.2 |  |
Deferred charges and other |  |  |  |  | 29.7 |  |  |  |  | 29.7 |  |
Total other assets |  |  |  |  | 426.1 |  |  |  |  | 426.1 |  |
Total assets |  |  |  |  | 5,128.2 |  |  |  |  | 5,128.2 |  |
Other current liabilities | 78.2 |  |  |  |  |  |  |  | 78.2 |  |  |
Total current liabilities | 335.6 |  |  |  |  |  |  |  | 335.6 |  |  |
Long-term debt, net (excluding current portion) |  |  |  |  | 1,543.3 |  |  |  |  | 1,543.3 |  |
Deferred tax liabilities | 1,010.8 |  |  |  | 970.0 |  |  |  | 1,010.8 | 970.0 |  |
Total other liabilities | 1,637.4 |  |  |  | 1,562.3 |  |  |  | 1,637.4 | 1,562.3 |  |
Retained earnings | 727.0 |  |  |  | 678.6 |  |  |  | 727.0 | 678.6 | 617.2 | 557.6
Total common equity | 1,752.2 |  |  |  | 1,703.8 |  |  |  | 1,752.2 | 1,703.8 |  |
Total equity | 1,763.5 |  |  |  | 1,712.3 |  |  |  | 1,763.5 | 1,712.3 |  |
Total liabilities and equity |  |  |  |  | 5,128.2 |  |  |  |  | 5,128.2 |  |
Income tax expense (benefit) |  |  |  |  |  |  |  |  |  | 85.6 | 87.2 |
Net income |  | 67.9 | 39.5 | 44.8 | 29.8 | 61.6 | 34.6 | 54.8 |  | 180.8 | 177.5 |
Net income (loss) attributable to common shareowners |  | $ 67.5 | $ 39.0 | $ 44.6 | 29.1 | $ 61.6 | $ 34.6 | $ 54.8 |  | 180.1 | 175.9 |
Deferred tax expense (benefit) and investment tax credits |  |  |  |  |  |  |  |  |  | 80.7 | 86.5 |
Other |  |  |  |  |  |  |  |  |  | (6.8) | (16.7) |
WPL [Member] | Restatement Adjustment [Member] |  |  |  |  |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Deferred tax assets |  |  |  |  | 0.2 |  |  |  |  | 0.2 |  |
Total current assets |  |  |  |  | 0.2 |  |  |  |  | 0.2 |  |
Total assets |  |  |  |  | 0.2 |  |  |  |  | 0.2 |  |
Other current liabilities | 1.3 |  |  |  |  |  |  |  | 1.3 |  |  |
Total current liabilities | 1.3 |  |  |  |  |  |  |  | 1.3 |  |  |
Deferred tax liabilities | (5.4) |  |  |  | (2.9) |  |  |  | (5.4) | (2.9) |  |
Total other liabilities | (5.4) |  |  |  | (2.9) |  |  |  | (5.4) | (2.9) |  |
Retained earnings | 4.1 |  |  |  | 3.1 |  |  |  | 4.1 | 3.1 | 5.0 | $ 8.3
Total common equity | 4.1 |  |  |  | 3.1 |  |  |  | 4.1 | 3.1 |  |
Total equity | $ 4.1 |  |  |  | 3.1 |  |  |  | $ 4.1 | 3.1 |  |
Total liabilities and equity |  |  |  |  | 0.2 |  |  |  |  | 0.2 |  |
Income tax expense (benefit) |  |  |  |  |  |  |  |  |  | (0.3) | (1.6) |
Net income |  |  |  |  |  |  |  |  |  | 0.3 | 1.6 |
Net income (loss) attributable to common shareowners |  |  |  |  |  |  |  |  |  | 0.3 | 1.6 |
Deferred tax expense (benefit) and investment tax credits |  |  |  |  |  |  |  |  |  | 1.9 | 3.3 |
Other |  |  |  |  |  |  |  |  |  | (2.2) | $ (4.9) |
WPL [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member] |  |  |  |  |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Deferred charges and other |  |  |  |  | (10.8) |  |  |  |  | (10.8) |  |
Total other assets |  |  |  |  | (10.8) |  |  |  |  | (10.8) |  |
Total assets |  |  |  |  | (10.8) |  |  |  |  | (10.8) |  |
Long-term debt, net (excluding current portion) |  |  |  |  | (10.8) |  |  |  |  | (10.8) |  |
Total liabilities and equity |  |  |  |  | $ (10.8) |  |  |  |  | $ (10.8) |  |

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