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v3.7.0.1

Fair Value Measurements (Fair Value Measurements) (Details) - USD ($) $ in Millions | Mar. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Assets: |  |
Deferred proceeds | $ 149.0 | $ 211.1
Liabilities and Equity: |  |
Long-term debt (including current maturities) | 4,771.2 | 4,799.0
Cumulative preferred stock of IPL | 202.6 | 194.8
IPL [Member] |  |
Assets: |  |
Deferred proceeds | 149.0 | 211.1
Liabilities and Equity: |  |
Long-term debt (including current maturities) | 2,342.1 | 2,352.3
Cumulative preferred stock of IPL | 202.6 | 194.8
WPL [Member] |  |
Liabilities and Equity: |  |
Long-term debt (including current maturities) | 1,790.9 | 1,807.4
Commodity Contracts [Member] |  |
Assets: |  |
Derivatives | 13.3 | 41.4
Liabilities and Equity: |  |
Derivatives | 45.3 | 28.6
Commodity Contracts [Member] | IPL [Member] |  |
Assets: |  |
Derivatives | 8.8 | 20.8
Liabilities and Equity: |  |
Derivatives | 16.3 | 8.3
Commodity Contracts [Member] | WPL [Member] |  |
Assets: |  |
Derivatives | 4.5 | 20.6
Liabilities and Equity: |  |
Derivatives | 29.0 | 20.3
Level 1 [Member] |  |
Assets: |  |
Deferred proceeds | 0.0 | 0.0
Liabilities and Equity: |  |
Long-term debt (including current maturities) | 0.0 | 0.0
Cumulative preferred stock of IPL | 202.6 | 194.8
Level 1 [Member] | IPL [Member] |  |
Assets: |  |
Deferred proceeds | 0.0 | 0.0
Liabilities and Equity: |  |
Long-term debt (including current maturities) | 0.0 | 0.0
Cumulative preferred stock of IPL | 202.6 | 194.8
Level 1 [Member] | WPL [Member] |  |
Liabilities and Equity: |  |
Long-term debt (including 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 (including current maturities) | 4,768.3 | 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 (including current maturities) | 2,342.1 | 2,352.3
Cumulative preferred stock of IPL | 0.0 | 0.0
Level 2 [Member] | WPL [Member] |  |
Liabilities and Equity: |  |
Long-term debt (including current maturities) | 1,790.9 | 1,807.4
Level 2 [Member] | Commodity Contracts [Member] |  |
Assets: |  |
Derivatives | 1.7 | 4.6
Liabilities and Equity: |  |
Derivatives | 0.8 | 0.5
Level 2 [Member] | Commodity Contracts [Member] | IPL [Member] |  |
Assets: |  |
Derivatives | 1.3 | 2.8
Liabilities and Equity: |  |
Derivatives | 0.5 | 0.4
Level 2 [Member] | Commodity Contracts [Member] | WPL [Member] |  |
Assets: |  |
Derivatives | 0.4 | 1.8
Liabilities and Equity: |  |
Derivatives | 0.3 | 0.1
Level 3 [Member] |  |
Assets: |  |
Deferred proceeds | 149.0 | 211.1
Liabilities and Equity: |  |
Long-term debt (including current maturities) | 2.9 | 3.3
Cumulative preferred stock of IPL | 0.0 | 0.0
Level 3 [Member] | IPL [Member] |  |
Assets: |  |
Deferred proceeds | 149.0 | 211.1
Liabilities and Equity: |  |
Long-term debt (including 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 (including current maturities) | 0.0 | 0.0
Level 3 [Member] | Commodity Contracts [Member] |  |
Assets: |  |
Derivatives | 11.6 | 36.8
Liabilities and Equity: |  |
Derivatives | 44.5 | 28.1
Level 3 [Member] | Commodity Contracts [Member] | IPL [Member] |  |
Assets: |  |
Derivatives | 7.5 | 18.0
Liabilities and Equity: |  |
Derivatives | 15.8 | 7.9
Level 3 [Member] | Commodity Contracts [Member] | WPL [Member] |  |
Assets: |  |
Derivatives | 4.1 | 18.8
Liabilities and Equity: |  |
Derivatives | 28.7 | 20.2
Carrying Amount [Member] |  |
Assets: |  |
Deferred proceeds | 149.0 | 211.1
Liabilities and Equity: |  |
Long-term debt (including current maturities) | 4,320.7 | 4,320.2
Cumulative preferred stock of IPL | 200.0 | 200.0
Carrying Amount [Member] | IPL [Member] |  |
Assets: |  |
Deferred proceeds | 149.0 | 211.1
Liabilities and Equity: |  |
Long-term debt (including current maturities) | 2,154.0 | 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) | 1,535.5 | 1,535.2
Carrying Amount [Member] | Commodity Contracts [Member] |  |
Assets: |  |
Derivatives | 13.3 | 41.4
Liabilities and Equity: |  |
Derivatives | 45.3 | 28.6
Carrying Amount [Member] | Commodity Contracts [Member] | IPL [Member] |  |
Assets: |  |
Derivatives | 8.8 | 20.8
Liabilities and Equity: |  |
Derivatives | 16.3 | 8.3
Carrying Amount [Member] | Commodity Contracts [Member] | WPL [Member] |  |
Assets: |  |
Derivatives | 4.5 | 20.6
Liabilities and Equity: |  |
Derivatives | $ 29.0 | $ 20.3

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