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v3.8.0.1

Fair Value Measurements (Fair Value Measurements) (Details) - USD ($) $ in Millions | Sep. 30, 2017 | Dec. 31, 2016
--- | --- | ---
Assets: |  |
Deferred proceeds | $ 115.3 | $ 211.1
Liabilities and Equity: |  |
Long-term debt (incl. current maturities) | 4,896.2 | 4,799.0
Cumulative preferred stock of IPL | 202.3 | 194.8
IPL [Member] |  |
Assets: |  |
Deferred proceeds | 115.3 | 211.1
Liabilities and Equity: |  |
Long-term debt (incl. current maturities) | 2,430.1 | 2,352.3
Cumulative preferred stock of IPL | 202.3 | 194.8
WPL [Member] |  |
Liabilities and Equity: |  |
Long-term debt (incl. current maturities) | 1,829.3 | 1,807.4
Commodity Contracts [Member] |  |
Assets: |  |
Derivatives | 29.4 | 41.4
Liabilities and Equity: |  |
Derivatives | 45.1 | 28.6
Commodity Contracts [Member] | IPL [Member] |  |
Assets: |  |
Derivatives | 21.1 | 20.8
Liabilities and Equity: |  |
Derivatives | 18.7 | 8.3
Commodity Contracts [Member] | WPL [Member] |  |
Assets: |  |
Derivatives | 8.3 | 20.6
Liabilities and Equity: |  |
Derivatives | 26.4 | 20.3
Level 1 [Member] |  |
Assets: |  |
Deferred proceeds | 0.0 | 0.0
Liabilities and Equity: |  |
Long-term debt (incl. current maturities) | 0.0 | 0.0
Cumulative preferred stock of IPL | 202.3 | 194.8
Level 1 [Member] | IPL [Member] |  |
Assets: |  |
Deferred proceeds | 0.0 | 0.0
Liabilities and Equity: |  |
Long-term debt (incl. current maturities) | 0.0 | 0.0
Cumulative preferred stock of IPL | 202.3 | 194.8
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: |  |
Deferred proceeds | 0.0 | 0.0
Liabilities and Equity: |  |
Long-term debt (incl. current maturities) | 4,893.3 | 4,795.7
Cumulative preferred stock of IPL | 0.0 | 0.0
Level 2 [Member] | IPL [Member] |  |
Assets: |  |
Deferred proceeds | 0.0 | 0.0
Liabilities and Equity: |  |
Long-term debt (incl. current maturities) | 2,430.1 | 2,352.3
Cumulative preferred stock of IPL | 0.0 | 0.0
Level 2 [Member] | WPL [Member] |  |
Liabilities and Equity: |  |
Long-term debt (incl. current maturities) | 1,829.3 | 1,807.4
Level 2 [Member] | Commodity Contracts [Member] |  |
Assets: |  |
Derivatives | 2.9 | 4.6
Liabilities and Equity: |  |
Derivatives | 14.9 | 0.5
Level 2 [Member] | Commodity Contracts [Member] | IPL [Member] |  |
Assets: |  |
Derivatives | 1.6 | 2.8
Liabilities and Equity: |  |
Derivatives | 4.5 | 0.4
Level 2 [Member] | Commodity Contracts [Member] | WPL [Member] |  |
Assets: |  |
Derivatives | 1.3 | 1.8
Liabilities and Equity: |  |
Derivatives | 10.4 | 0.1
Level 3 [Member] |  |
Assets: |  |
Deferred proceeds | 115.3 | 211.1
Liabilities and Equity: |  |
Long-term debt (incl. current maturities) | 2.9 | 3.3
Cumulative preferred stock of IPL | 0.0 | 0.0
Level 3 [Member] | IPL [Member] |  |
Assets: |  |
Deferred proceeds | 115.3 | 211.1
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 | 26.5 | 36.8
Liabilities and Equity: |  |
Derivatives | 30.2 | 28.1
Level 3 [Member] | Commodity Contracts [Member] | IPL [Member] |  |
Assets: |  |
Derivatives | 19.5 | 18.0
Liabilities and Equity: |  |
Derivatives | 14.2 | 7.9
Level 3 [Member] | Commodity Contracts [Member] | WPL [Member] |  |
Assets: |  |
Derivatives | 7.0 | 18.8
Liabilities and Equity: |  |
Derivatives | 16.0 | 20.2
Carrying Amount [Member] |  |
Assets: |  |
Deferred proceeds | 115.3 | 211.1
Liabilities and Equity: |  |
Long-term debt (including current maturities) | 4,360.3 | 4,320.2
Cumulative preferred stock of IPL | 200.0 | 200.0
Carrying Amount [Member] | IPL [Member] |  |
Assets: |  |
Deferred proceeds | 115.3 | 211.1
Liabilities and Equity: |  |
Long-term debt (including current maturities) | 2,195.0 | 2,153.5
Cumulative preferred stock of IPL | 200.0 | 200.0
Carrying Amount [Member] | WPL [Member] |  |
Liabilities and Equity: |  |
Long-term debt (including current maturities) | 1,536.2 | 1,535.2
Carrying Amount [Member] | Commodity Contracts [Member] |  |
Assets: |  |
Derivatives | 29.4 | 41.4
Liabilities and Equity: |  |
Derivatives | 45.1 | 28.6
Carrying Amount [Member] | Commodity Contracts [Member] | IPL [Member] |  |
Assets: |  |
Derivatives | 21.1 | 20.8
Liabilities and Equity: |  |
Derivatives | 18.7 | 8.3
Carrying Amount [Member] | Commodity Contracts [Member] | WPL [Member] |  |
Assets: |  |
Derivatives | 8.3 | 20.6
Liabilities and Equity: |  |
Derivatives | $ 26.4 | $ 20.3

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