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Benefit Plans (Fair Value Of Plan Assets By Asset Category And Fair Value Hierarchy Level) (Details) - USD ($) $ in Millions | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | --- | ---
Pension Plans, Defined Benefit [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | $ 930.4 | $ 808.6 | $ 950.7
Assets measured at net asset value | 410.1 | 355.4 |
Pension Plans, Defined Benefit [Member] | Cash and equivalents [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 45.7 | 36.4 |
Pension Plans, Defined Benefit [Member] | Cash and equivalents [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 3.7 | 3.0 |
Pension Plans, Defined Benefit [Member] | Cash and equivalents [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 42.0 | 33.4 |
Pension Plans, Defined Benefit [Member] | Cash and equivalents [Member] | Level 3 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Pension Plans, Defined Benefit [Member] | Equity securites - U.S. [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 160.6 | 130.2 |
Pension Plans, Defined Benefit [Member] | Equity securites - U.S. [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 160.6 | 130.2 |
Pension Plans, Defined Benefit [Member] | Equity securites - U.S. [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Pension Plans, Defined Benefit [Member] | Equity securites - U.S. [Member] | Level 3 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Pension Plans, Defined Benefit [Member] | Equity securities - international [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 135.9 | 116.0 |
Pension Plans, Defined Benefit [Member] | Equity securities - international [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 135.9 | 116.0 |
Pension Plans, Defined Benefit [Member] | Equity securities - international [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Pension Plans, Defined Benefit [Member] | Equity securities - international [Member] | Level 3 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Pension Plans, Defined Benefit [Member] | Global asset securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 47.2 | 42.1 |
Pension Plans, Defined Benefit [Member] | Global asset securities [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 47.2 | 42.1 |
Pension Plans, Defined Benefit [Member] | Global asset securities [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Pension Plans, Defined Benefit [Member] | Global asset securities [Member] | Level 3 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Pension Plans, Defined Benefit [Member] | Fixed income securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 130.7 | 127.8 |
Pension Plans, Defined Benefit [Member] | Fixed income securities [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 58.0 | 52.5 |
Pension Plans, Defined Benefit [Member] | Fixed income securities [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 72.7 | 75.3 |
Pension Plans, Defined Benefit [Member] | Fixed income securities [Member] | Level 3 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Pension Plans, Defined Benefit [Member] | Subtotal [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total assets in fair value hierarchy | 520.1 | 452.5 |
Pension Plans, Defined Benefit [Member] | Subtotal [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 405.4 | 343.8 |
Pension Plans, Defined Benefit [Member] | Subtotal [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 114.7 | 108.7 |
Pension Plans, Defined Benefit [Member] | Subtotal [Member] | Level 3 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Pension Plans, Defined Benefit [Member] | Accrued investment income [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.9 | 1.2 |
Pension Plans, Defined Benefit [Member] | IPL [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 436.0 | 377.8 | 443.7
Assets measured at net asset value | 192.2 | 166.1 |
Pension Plans, Defined Benefit [Member] | IPL [Member] | Cash and equivalents [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 21.4 | 17.0 |
Pension Plans, Defined Benefit [Member] | IPL [Member] | Cash and equivalents [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 1.7 | 1.4 |
Pension Plans, Defined Benefit [Member] | IPL [Member] | Cash and equivalents [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 19.7 | 15.6 |
Pension Plans, Defined Benefit [Member] | IPL [Member] | Cash and equivalents [Member] | Level 3 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Pension Plans, Defined Benefit [Member] | IPL [Member] | Equity securites - U.S. [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 75.2 | 60.8 |
Pension Plans, Defined Benefit [Member] | IPL [Member] | Equity securites - U.S. [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 75.2 | 60.8 |
Pension Plans, Defined Benefit [Member] | IPL [Member] | Equity securites - U.S. [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Pension Plans, Defined Benefit [Member] | IPL [Member] | Equity securites - U.S. [Member] | Level 3 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Pension Plans, Defined Benefit [Member] | IPL [Member] | Equity securities - international [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 63.7 | 54.2 |
Pension Plans, Defined Benefit [Member] | IPL [Member] | Equity securities - international [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 63.7 | 54.2 |
Pension Plans, Defined Benefit [Member] | IPL [Member] | Equity securities - international [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Pension Plans, Defined Benefit [Member] | IPL [Member] | Equity securities - international [Member] | Level 3 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Pension Plans, Defined Benefit [Member] | IPL [Member] | Global asset securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 22.1 | 19.7 |
Pension Plans, Defined Benefit [Member] | IPL [Member] | Global asset securities [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 22.1 | 19.7 |
Pension Plans, Defined Benefit [Member] | IPL [Member] | Global asset securities [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Pension Plans, Defined Benefit [Member] | IPL [Member] | Global asset securities [Member] | Level 3 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Pension Plans, Defined Benefit [Member] | IPL [Member] | Fixed income securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 61.3 | 59.7 |
Pension Plans, Defined Benefit [Member] | IPL [Member] | Fixed income securities [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 27.2 | 24.5 |
Pension Plans, Defined Benefit [Member] | IPL [Member] | Fixed income securities [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 34.1 | 35.2 |
Pension Plans, Defined Benefit [Member] | IPL [Member] | Fixed income securities [Member] | Level 3 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Pension Plans, Defined Benefit [Member] | IPL [Member] | Subtotal [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total assets in fair value hierarchy | 243.7 | 211.4 |
Pension Plans, Defined Benefit [Member] | IPL [Member] | Subtotal [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 189.9 | 160.6 |
Pension Plans, Defined Benefit [Member] | IPL [Member] | Subtotal [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 53.8 | 50.8 |
Pension Plans, Defined Benefit [Member] | IPL [Member] | Subtotal [Member] | Level 3 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Pension Plans, Defined Benefit [Member] | IPL [Member] | Accrued investment income [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.4 | 0.6 |
Pension Plans, Defined Benefit [Member] | WPL [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 406.0 | 352.2 | 415.0
Assets measured at net asset value | 179.0 | 154.8 |
Pension Plans, Defined Benefit [Member] | WPL [Member] | Cash and equivalents [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 19.9 | 15.9 |
Pension Plans, Defined Benefit [Member] | WPL [Member] | Cash and equivalents [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 1.6 | 1.3 |
Pension Plans, Defined Benefit [Member] | WPL [Member] | Cash and equivalents [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 18.3 | 14.6 |
Pension Plans, Defined Benefit [Member] | WPL [Member] | Cash and equivalents [Member] | Level 3 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Pension Plans, Defined Benefit [Member] | WPL [Member] | Equity securites - U.S. [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 70.1 | 56.7 |
Pension Plans, Defined Benefit [Member] | WPL [Member] | Equity securites - U.S. [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 70.1 | 56.7 |
Pension Plans, Defined Benefit [Member] | WPL [Member] | Equity securites - U.S. [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Pension Plans, Defined Benefit [Member] | WPL [Member] | Equity securites - U.S. [Member] | Level 3 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Pension Plans, Defined Benefit [Member] | WPL [Member] | Equity securities - international [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 59.3 | 50.5 |
Pension Plans, Defined Benefit [Member] | WPL [Member] | Equity securities - international [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 59.3 | 50.5 |
Pension Plans, Defined Benefit [Member] | WPL [Member] | Equity securities - international [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Pension Plans, Defined Benefit [Member] | WPL [Member] | Equity securities - international [Member] | Level 3 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Pension Plans, Defined Benefit [Member] | WPL [Member] | Global asset securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 20.6 | 18.4 |
Pension Plans, Defined Benefit [Member] | WPL [Member] | Global asset securities [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 20.6 | 18.4 |
Pension Plans, Defined Benefit [Member] | WPL [Member] | Global asset securities [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Pension Plans, Defined Benefit [Member] | WPL [Member] | Global asset securities [Member] | Level 3 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Pension Plans, Defined Benefit [Member] | WPL [Member] | Fixed income securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 57.0 | 55.6 |
Pension Plans, Defined Benefit [Member] | WPL [Member] | Fixed income securities [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 25.3 | 22.8 |
Pension Plans, Defined Benefit [Member] | WPL [Member] | Fixed income securities [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 31.7 | 32.8 |
Pension Plans, Defined Benefit [Member] | WPL [Member] | Fixed income securities [Member] | Level 3 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Pension Plans, Defined Benefit [Member] | WPL [Member] | Subtotal [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total assets in fair value hierarchy | 226.9 | 197.1 |
Pension Plans, Defined Benefit [Member] | WPL [Member] | Subtotal [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 176.9 | 149.7 |
Pension Plans, Defined Benefit [Member] | WPL [Member] | Subtotal [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 50.0 | 47.4 |
Pension Plans, Defined Benefit [Member] | WPL [Member] | Subtotal [Member] | Level 3 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Pension Plans, Defined Benefit [Member] | WPL [Member] | Accrued investment income [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.4 | 0.5 |
Other Postretirement Benefit Plans, Defined Benefit [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 104.9 | 99.1 | 111.1
Assets measured at net asset value | 26.0 | 22.3 |
Total assets in fair value hierarchy | 78.9 | 76.8 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 77.8 | 75.8 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 1.1 | 1.0 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | Level 3 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | Cash and equivalents [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 3.4 | 1.4 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | Cash and equivalents [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 3.0 | 1.1 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | Cash and equivalents [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.4 | 0.3 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | Cash and equivalents [Member] | Level 3 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity securites - U.S. [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 3.7 | 3.9 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity securites - U.S. [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 3.7 | 3.9 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity securites - U.S. [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity securites - U.S. [Member] | Level 3 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity securities - international [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 2.8 | 2.9 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity securities - international [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 2.8 | 2.9 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity securities - international [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity securities - international [Member] | Level 3 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | Global asset securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.5 | 0.4 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | Global asset securities [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.5 | 0.4 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | Global asset securities [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | Global asset securities [Member] | Level 3 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fixed income securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 68.5 | 68.2 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fixed income securities [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 67.8 | 67.5 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fixed income securities [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.7 | 0.7 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fixed income securities [Member] | Level 3 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 71.9 | 66.7 | 72.9
Assets measured at net asset value | 22.1 | 19.0 |
Total assets in fair value hierarchy | 49.8 | 47.7 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 49.8 | 47.7 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Level 3 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Cash and equivalents [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 1.5 | 0.7 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Cash and equivalents [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 1.5 | 0.7 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Cash and equivalents [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Cash and equivalents [Member] | Level 3 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Fixed income securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 48.3 | 47.0 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Fixed income securities [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 48.3 | 47.0 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Fixed income securities [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Fixed income securities [Member] | Level 3 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 17.1 | 16.7 | $ 18.7
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 17.1 | 16.7 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Level 3 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Cash and equivalents [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.4 | 0.1 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Cash and equivalents [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.4 | 0.1 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Cash and equivalents [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Cash and equivalents [Member] | Level 3 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Fixed income securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 16.7 | 16.6 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Fixed income securities [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 16.7 | 16.6 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Fixed income securities [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Fixed income securities [Member] | Level 3 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 0.0 |
Defined Benefit Plan Due To Brokers Net [Member] | Pension Plans, Defined Benefit [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | (0.7) | (0.5) |
Defined Benefit Plan Due To Brokers Net [Member] | Pension Plans, Defined Benefit [Member] | IPL [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | (0.3) | (0.3) |
Defined Benefit Plan Due To Brokers Net [Member] | Pension Plans, Defined Benefit [Member] | WPL [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | $ (0.3) | $ (0.2) |

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