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v3.19.1

Fair Value Measurements (Fair Value Measurements) (Details) - USD ($) $ in Millions | Mar. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Assets: |  |
Deferred proceeds | $ 178.3 | $ 119.4
Liabilities: |  |
Long-term debt (incl. current maturities) | 6,073.7 | 5,860.8
IPL [Member] |  |
Assets: |  |
Deferred proceeds | 178.3 | 119.4
Liabilities: |  |
Long-term debt (incl. current maturities) | 2,852.4 | 2,691.2
WPL [Member] |  |
Liabilities: |  |
Long-term debt (incl. current maturities) | 2,080.0 | 2,043.7
Commodity Contracts [Member] |  |
Assets: |  |
Derivatives | 21.7 | 28.3
Liabilities: |  |
Derivatives | 15.7 | 23.3
Commodity Contracts [Member] | IPL [Member] |  |
Assets: |  |
Derivatives | 11.9 | 17.7
Liabilities: |  |
Derivatives | 7.1 | 11.2
Commodity Contracts [Member] | WPL [Member] |  |
Assets: |  |
Derivatives | 9.8 | 10.6
Liabilities: |  |
Derivatives | 8.6 | 12.1
Level 1 [Member] |  |
Assets: |  |
Deferred proceeds | 0.0 | 0.0
Liabilities: |  |
Long-term debt (incl. current maturities) | 0.0 | 0.0
Level 1 [Member] | IPL [Member] |  |
Assets: |  |
Deferred proceeds | 0.0 | 0.0
Liabilities: |  |
Long-term debt (incl. current maturities) | 0.0 | 0.0
Level 1 [Member] | WPL [Member] |  |
Liabilities: |  |
Long-term debt (incl. current maturities) | 0.0 | 0.0
Level 1 [Member] | Commodity Contracts [Member] |  |
Assets: |  |
Derivatives | 0.0 | 0.0
Liabilities: |  |
Derivatives | 0.0 | 0.0
Level 1 [Member] | Commodity Contracts [Member] | IPL [Member] |  |
Assets: |  |
Derivatives | 0.0 | 0.0
Liabilities: |  |
Derivatives | 0.0 | 0.0
Level 1 [Member] | Commodity Contracts [Member] | WPL [Member] |  |
Assets: |  |
Derivatives | 0.0 | 0.0
Liabilities: |  |
Derivatives | 0.0 | 0.0
Level 2 [Member] |  |
Assets: |  |
Deferred proceeds | 0.0 | 0.0
Liabilities: |  |
Long-term debt (incl. current maturities) | 6,071.6 | 5,858.4
Level 2 [Member] | IPL [Member] |  |
Assets: |  |
Deferred proceeds | 0.0 | 0.0
Liabilities: |  |
Long-term debt (incl. current maturities) | 2,852.4 | 2,691.2
Level 2 [Member] | WPL [Member] |  |
Liabilities: |  |
Long-term debt (incl. current maturities) | 2,080.0 | 2,043.7
Level 2 [Member] | Commodity Contracts [Member] |  |
Assets: |  |
Derivatives | 15.9 | 8.9
Liabilities: |  |
Derivatives | 10.3 | 16.1
Level 2 [Member] | Commodity Contracts [Member] | IPL [Member] |  |
Assets: |  |
Derivatives | 7.7 | 4.0
Liabilities: |  |
Derivatives | 3.5 | 6.5
Level 2 [Member] | Commodity Contracts [Member] | WPL [Member] |  |
Assets: |  |
Derivatives | 8.2 | 4.9
Liabilities: |  |
Derivatives | 6.8 | 9.6
Level 3 [Member] |  |
Assets: |  |
Deferred proceeds | 178.3 | 119.4
Liabilities: |  |
Long-term debt (incl. current maturities) | 2.1 | 2.4
Level 3 [Member] | IPL [Member] |  |
Assets: |  |
Deferred proceeds | 178.3 | 119.4
Liabilities: |  |
Long-term debt (incl. current maturities) | 0.0 | 0.0
Level 3 [Member] | WPL [Member] |  |
Liabilities: |  |
Long-term debt (incl. current maturities) | 0.0 | 0.0
Level 3 [Member] | Commodity Contracts [Member] |  |
Assets: |  |
Derivatives | 5.8 | 19.4
Liabilities: |  |
Derivatives | 5.4 | 7.2
Level 3 [Member] | Commodity Contracts [Member] | IPL [Member] |  |
Assets: |  |
Derivatives | 4.2 | 13.7
Liabilities: |  |
Derivatives | 3.6 | 4.7
Level 3 [Member] | Commodity Contracts [Member] | WPL [Member] |  |
Assets: |  |
Derivatives | 1.6 | 5.7
Liabilities: |  |
Derivatives | 1.8 | 2.5
Carrying Amount [Member] |  |
Assets: |  |
Deferred proceeds | 178.3 | 119.4
Liabilities: |  |
Long-term debt (incl. current maturities) | 5,618.7 | 5,502.8
Carrying Amount [Member] | IPL [Member] |  |
Assets: |  |
Deferred proceeds | 178.3 | 119.4
Liabilities: |  |
Long-term debt (incl. current maturities) | 2,667.8 | 2,552.3
Carrying Amount [Member] | WPL [Member] |  |
Liabilities: |  |
Long-term debt (incl. current maturities) | 1,835.4 | 1,834.9
Carrying Amount [Member] | Commodity Contracts [Member] |  |
Assets: |  |
Derivatives | 21.7 | 28.3
Liabilities: |  |
Derivatives | 15.7 | 23.3
Carrying Amount [Member] | Commodity Contracts [Member] | IPL [Member] |  |
Assets: |  |
Derivatives | 11.9 | 17.7
Liabilities: |  |
Derivatives | 7.1 | 11.2
Carrying Amount [Member] | Commodity Contracts [Member] | WPL [Member] |  |
Assets: |  |
Derivatives | 9.8 | 10.6
Liabilities: |  |
Derivatives | $ 8.6 | $ 12.1

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