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Income Taxes (Schedule Of Deferred Tax Assets And Liabilities) (Details) - USD ($) $ in Millions | Dec. 31, 2015 | Dec. 31, 2014
--- | --- | ---
Deferred tax assets, gross | $ (677.1) | $ (768.5)
Deferred tax liabilities, gross | 3,058.3 | 2,939.5
Deferred tax (assets) and liabilities, net | 2,381.2 | 2,171.0
Current deferred tax assets | 0.0 | (150.1)
Non-current deferred tax liabilities | 2,381.2 | 2,321.1
Deferred tax liabilities, net of deferred tax assets | 2,381.2 | 2,171.0
IPL [Member] |  |
Deferred tax assets, gross | (297.6) | (362.3)
Deferred tax liabilities, gross | 1,675.6 | 1,628.6
Deferred tax (assets) and liabilities, net | 1,378.0 | 1,266.3
Current deferred tax assets | 0.0 | (104.0)
Non-current deferred tax liabilities | 1,378.0 | 1,370.3
Deferred tax liabilities, net of deferred tax assets | 1,378.0 | 1,266.3
WPL [Member] |  |
Deferred tax assets, gross | (228.4) | (245.4)
Deferred tax liabilities, gross | 1,233.8 | 1,174.8
Deferred tax (assets) and liabilities, net | 1,005.4 | 929.4
Current deferred tax assets | 0.0 | (37.7)
Non-current deferred tax liabilities | 1,005.4 | 967.1
Deferred tax liabilities, net of deferred tax assets | 1,005.4 | 929.4
Property [Member] |  |
Deferred tax assets, gross | 0.0 | 0.0
Deferred tax liabilities, gross | 2,762.9 | 2,627.8
Deferred tax (assets) and liabilities, net | 2,762.9 | 2,627.8
Property [Member] | IPL [Member] |  |
Deferred tax assets, gross | 0.0 | 0.0
Deferred tax liabilities, gross | 1,587.8 | 1,545.1
Deferred tax (assets) and liabilities, net | 1,587.8 | 1,545.1
Property [Member] | WPL [Member] |  |
Deferred tax assets, gross | 0.0 | 0.0
Deferred tax liabilities, gross | 1,027.0 | 963.0
Deferred tax (assets) and liabilities, net | 1,027.0 | 963.0
Investment In ATC [Member] |  |
Deferred tax assets, gross | 0.0 | 0.0
Deferred tax liabilities, gross | 138.1 | 131.6
Deferred tax (assets) and liabilities, net | 138.1 | 131.6
Investment In ATC [Member] | WPL [Member] |  |
Deferred tax assets, gross | 0.0 | 0.0
Deferred tax liabilities, gross | 138.9 | 132.1
Deferred tax (assets) and liabilities, net | 138.9 | 132.1
Net operating losses carryforward - state [Member] |  |
Deferred tax assets, gross | (38.3) | (45.7)
Deferred tax liabilities, gross | 0.0 | 0.0
Deferred tax (assets) and liabilities, net | (38.3) | (45.7)
Regulatory liability - IPL's tax benefit riders [Member] |  |
Deferred tax assets, gross | (66.1) | (100.9)
Deferred tax liabilities, gross | 0.0 | 0.0
Deferred tax (assets) and liabilities, net | (66.1) | (100.9)
Regulatory liability - IPL's tax benefit riders [Member] | IPL [Member] |  |
Deferred tax assets, gross | (66.1) | (100.9)
Deferred tax liabilities, gross | 0.0 | 0.0
Deferred tax (assets) and liabilities, net | (66.1) | (100.9)
Federal credit carryforwards [Member] |  |
Deferred tax assets, gross | (236.4) | (201.0)
Deferred tax liabilities, gross | 0.0 | 0.0
Deferred tax (assets) and liabilities, net | (236.4) | (201.0)
Federal credit carryforwards [Member] | IPL [Member] |  |
Deferred tax assets, gross | (81.7) | (66.5)
Deferred tax liabilities, gross | 0.0 | 0.0
Deferred tax (assets) and liabilities, net | (81.7) | (66.5)
Federal credit carryforwards [Member] | WPL [Member] |  |
Deferred tax assets, gross | (95.5) | (76.7)
Deferred tax liabilities, gross | 0.0 | 0.0
Deferred tax (assets) and liabilities, net | (95.5) | (76.7)
Net operating losses carryforwards - federal [Member] |  |
Deferred tax assets, gross | (250.9) | (332.8)
Deferred tax liabilities, gross | 0.0 | 0.0
Deferred tax (assets) and liabilities, net | (250.9) | (332.8)
Net operating losses carryforwards - federal [Member] | IPL [Member] |  |
Deferred tax assets, gross | (113.1) | (157.8)
Deferred tax liabilities, gross | 0.0 | 0.0
Deferred tax (assets) and liabilities, net | (113.1) | (157.8)
Net operating losses carryforwards - federal [Member] | WPL [Member] |  |
Deferred tax assets, gross | (105.1) | (131.6)
Deferred tax liabilities, gross | 0.0 | 0.0
Deferred tax (assets) and liabilities, net | (105.1) | (131.6)
Other [Member] |  |
Deferred tax assets, gross | (85.4) | (88.1)
Deferred tax liabilities, gross | 157.3 | 180.1
Deferred tax (assets) and liabilities, net | 71.9 | 92.0
Other [Member] | IPL [Member] |  |
Deferred tax assets, gross | (36.7) | (37.1)
Deferred tax liabilities, gross | 87.8 | 83.5
Deferred tax (assets) and liabilities, net | 51.1 | 46.4
Other [Member] | WPL [Member] |  |
Deferred tax assets, gross | (27.8) | (37.1)
Deferred tax liabilities, gross | 67.9 | 79.7
Deferred tax (assets) and liabilities, net | $ 40.1 | $ 42.6

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