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v3.10.0.1

Fair Value Measurements (Fair Value Measurements) (Details) - USD ($) $ in Millions | Sep. 30, 2018 | Dec. 31, 2017
--- | --- | ---
Assets: |  |
Money market fund investments | $ 228.0 | $ 0.0
Deferred proceeds | 243.7 | 222.1
Liabilities and Equity: |  |
Long-term debt (incl. current maturities) | 6,060.3 | 5,447.5
Cumulative preferred stock of IPL | 200.0 | 203.8
IPL [Member] |  |
Assets: |  |
Money market fund investments | 228.0 | 0.0
Deferred proceeds | 243.7 | 222.1
Liabilities and Equity: |  |
Long-term debt (incl. current maturities) | 2,916.2 | 2,665.7
Cumulative preferred stock of IPL | 200.0 | 203.8
WPL [Member] |  |
Liabilities and Equity: |  |
Long-term debt (incl. current maturities) | 2,020.9 | 2,147.9
Commodity Contracts [Member] |  |
Assets: |  |
Derivatives | 48.0 | 25.1
Liabilities and Equity: |  |
Derivatives | 22.0 | 41.7
Commodity Contracts [Member] | IPL [Member] |  |
Assets: |  |
Derivatives | 29.1 | 17.1
Liabilities and Equity: |  |
Derivatives | 9.7 | 19.4
Commodity Contracts [Member] | WPL [Member] |  |
Assets: |  |
Derivatives | 18.9 | 8.0
Liabilities and Equity: |  |
Derivatives | 12.3 | 22.3
Level 1 [Member] |  |
Assets: |  |
Money market fund investments | 228.0 | 0.0
Deferred proceeds | 0.0 | 0.0
Liabilities and Equity: |  |
Long-term debt (incl. current maturities) | 0.0 | 0.0
Cumulative preferred stock of IPL | 200.0 | 203.8
Level 1 [Member] | IPL [Member] |  |
Assets: |  |
Money market fund investments | 228.0 | 0.0
Deferred proceeds | 0.0 | 0.0
Liabilities and Equity: |  |
Long-term debt (incl. current maturities) | 0.0 | 0.0
Cumulative preferred stock of IPL | 200.0 | 203.8
Level 1 [Member] | WPL [Member] |  |
Liabilities and Equity: |  |
Long-term debt (incl. current maturities) | 0.0 | 0.0
Level 1 [Member] | Commodity Contracts [Member] |  |
Assets: |  |
Derivatives | 0.0 | 0.0
Liabilities and Equity: |  |
Derivatives | 0.0 | 0.0
Level 1 [Member] | Commodity Contracts [Member] | IPL [Member] |  |
Assets: |  |
Derivatives | 0.0 | 0.0
Liabilities and Equity: |  |
Derivatives | 0.0 | 0.0
Level 1 [Member] | Commodity Contracts [Member] | WPL [Member] |  |
Assets: |  |
Derivatives | 0.0 | 0.0
Liabilities and Equity: |  |
Derivatives | 0.0 | 0.0
Level 2 [Member] |  |
Assets: |  |
Money market fund investments | 0.0 | 0.0
Deferred proceeds | 0.0 | 0.0
Liabilities and Equity: |  |
Long-term debt (incl. current maturities) | 6,057.8 | 5,444.6
Cumulative preferred stock of IPL | 0.0 | 0.0
Level 2 [Member] | IPL [Member] |  |
Assets: |  |
Money market fund investments | 0.0 | 0.0
Deferred proceeds | 0.0 | 0.0
Liabilities and Equity: |  |
Long-term debt (incl. current maturities) | 2,916.2 | 2,665.7
Cumulative preferred stock of IPL | 0.0 | 0.0
Level 2 [Member] | WPL [Member] |  |
Liabilities and Equity: |  |
Long-term debt (incl. current maturities) | 2,020.9 | 2,147.9
Level 2 [Member] | Commodity Contracts [Member] |  |
Assets: |  |
Derivatives | 16.5 | 4.1
Liabilities and Equity: |  |
Derivatives | 14.7 | 8.5
Level 2 [Member] | Commodity Contracts [Member] | IPL [Member] |  |
Assets: |  |
Derivatives | 6.7 | 2.0
Liabilities and Equity: |  |
Derivatives | 5.5 | 2.9
Level 2 [Member] | Commodity Contracts [Member] | WPL [Member] |  |
Assets: |  |
Derivatives | 9.8 | 2.1
Liabilities and Equity: |  |
Derivatives | 9.2 | 5.6
Level 3 [Member] |  |
Assets: |  |
Money market fund investments | 0.0 | 0.0
Deferred proceeds | 243.7 | 222.1
Liabilities and Equity: |  |
Long-term debt (incl. current maturities) | 2.5 | 2.9
Cumulative preferred stock of IPL | 0.0 | 0.0
Level 3 [Member] | IPL [Member] |  |
Assets: |  |
Money market fund investments | 0.0 | 0.0
Deferred proceeds | 243.7 | 222.1
Liabilities and Equity: |  |
Long-term debt (incl. current maturities) | 0.0 | 0.0
Cumulative preferred stock of IPL | 0.0 | 0.0
Level 3 [Member] | WPL [Member] |  |
Liabilities and Equity: |  |
Long-term debt (incl. current maturities) | 0.0 | 0.0
Level 3 [Member] | Commodity Contracts [Member] |  |
Assets: |  |
Derivatives | 31.5 | 21.0
Liabilities and Equity: |  |
Derivatives | 7.3 | 33.2
Level 3 [Member] | Commodity Contracts [Member] | IPL [Member] |  |
Assets: |  |
Derivatives | 22.4 | 15.1
Liabilities and Equity: |  |
Derivatives | 4.2 | 16.5
Level 3 [Member] | Commodity Contracts [Member] | WPL [Member] |  |
Assets: |  |
Derivatives | 9.1 | 5.9
Liabilities and Equity: |  |
Derivatives | 3.1 | 16.7
Carrying Amount [Member] |  |
Assets: |  |
Money market fund investments | 228.0 | 0.0
Deferred proceeds | 243.7 | 222.1
Liabilities and Equity: |  |
Long-term debt (incl. current maturities) | 5,754.3 | 4,866.3
Cumulative preferred stock of IPL | 200.0 | 200.0
Carrying Amount [Member] | IPL [Member] |  |
Assets: |  |
Money market fund investments | 228.0 | 0.0
Deferred proceeds | 243.7 | 222.1
Liabilities and Equity: |  |
Long-term debt (incl. current maturities) | 2,801.8 | 2,406.0
Cumulative preferred stock of IPL | 200.0 | 200.0
Carrying Amount [Member] | WPL [Member] |  |
Liabilities and Equity: |  |
Long-term debt (incl. current maturities) | 1,834.5 | 1,833.4
Carrying Amount [Member] | Commodity Contracts [Member] |  |
Assets: |  |
Derivatives | 48.0 | 25.1
Liabilities and Equity: |  |
Derivatives | 22.0 | 41.7
Carrying Amount [Member] | Commodity Contracts [Member] | IPL [Member] |  |
Assets: |  |
Derivatives | 29.1 | 17.1
Liabilities and Equity: |  |
Derivatives | 9.7 | 19.4
Carrying Amount [Member] | Commodity Contracts [Member] | WPL [Member] |  |
Assets: |  |
Derivatives | 18.9 | 8.0
Liabilities and Equity: |  |
Derivatives | $ 12.3 | $ 22.3

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