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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, 2018 | Dec. 31, 2017 | Dec. 31, 2016
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Pension Plans, Defined Benefit [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | $ 808.6 | $ 950.7 | $ 895.7
Assets measured at net asset value | 355.4 | 441.1 |
Total assets in fair value hierarchy | 808.6 | 950.7 |
Pension Plans, Defined Benefit [Member] | Cash and equivalents [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 36.4 | 28.2 |
Pension Plans, Defined Benefit [Member] | Cash and equivalents [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 3.0 | 4.5 |
Pension Plans, Defined Benefit [Member] | Cash and equivalents [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 33.4 | 23.7 |
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 | 130.2 | 158.3 |
Pension Plans, Defined Benefit [Member] | Equity securites - U.S. [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 130.2 | 158.3 |
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 | 116.0 | 137.5 |
Pension Plans, Defined Benefit [Member] | Equity securities - international [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 116.0 | 137.5 |
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 | 42.1 | 49.4 |
Pension Plans, Defined Benefit [Member] | Global asset securities [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 42.1 | 49.4 |
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 | 127.8 | 135.9 |
Pension Plans, Defined Benefit [Member] | Fixed income securities [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 52.5 | 55.8 |
Pension Plans, Defined Benefit [Member] | Fixed income securities [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 75.3 | 80.1 |
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 | 452.5 | 509.3 |
Pension Plans, Defined Benefit [Member] | Subtotal [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 343.8 | 405.5 |
Pension Plans, Defined Benefit [Member] | Subtotal [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 108.7 | 103.8 |
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 | 1.2 | 1.0 |
Pension Plans, Defined Benefit [Member] | IPL [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 377.8 | 443.7 | 422.0
Assets measured at net asset value | 166.1 | 205.8 |
Total assets in fair value hierarchy | 377.8 | 443.7 |
Pension Plans, Defined Benefit [Member] | IPL [Member] | Cash and equivalents [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 17.0 | 13.2 |
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 | 1.4 | 2.2 |
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 | 15.6 | 11.0 |
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 | 60.8 | 73.9 |
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 | 60.8 | 73.9 |
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 | 54.2 | 64.2 |
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 | 54.2 | 64.2 |
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 | 19.7 | 23.0 |
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 | 19.7 | 23.0 |
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 | 59.7 | 63.4 |
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 | 24.5 | 26.0 |
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 | 35.2 | 37.4 |
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 | 211.4 | 237.7 |
Pension Plans, Defined Benefit [Member] | IPL [Member] | Subtotal [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 160.6 | 189.3 |
Pension Plans, Defined Benefit [Member] | IPL [Member] | Subtotal [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 50.8 | 48.4 |
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 | 0.6 | 0.5 |
Pension Plans, Defined Benefit [Member] | WPL [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 352.2 | 415.0 | 389.7
Assets measured at net asset value | 154.8 | 192.5 |
Total assets in fair value hierarchy | 352.2 | 415.0 |
Pension Plans, Defined Benefit [Member] | WPL [Member] | Cash and equivalents [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 15.9 | 12.3 |
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 | 1.3 | 2.0 |
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 | 14.6 | 10.3 |
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 | 56.7 | 69.1 |
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 | 56.7 | 69.1 |
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 | 50.5 | 60.0 |
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 | 50.5 | 60.0 |
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 | 18.4 | 21.6 |
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 | 18.4 | 21.6 |
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 | 55.6 | 59.3 |
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 | 22.8 | 24.3 |
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 | 32.8 | 35.0 |
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 | 197.1 | 222.3 |
Pension Plans, Defined Benefit [Member] | WPL [Member] | Subtotal [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 149.7 | 177.0 |
Pension Plans, Defined Benefit [Member] | WPL [Member] | Subtotal [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 47.4 | 45.3 |
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 | 0.5 | 0.5 |
Other Postretirement Benefit Plans, Defined Benefit [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 99.1 | 111.1 | 105.8
Assets measured at net asset value | 22.3 | 3.6 |
Total assets in fair value hierarchy | 76.8 | 107.5 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 75.8 | 106.4 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 1.0 | 1.1 |
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 | 1.4 | 1.2 |
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 | 1.1 | 0.7 |
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 | 0.3 | 0.5 |
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 | 3.9 | 27.9 |
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 | 3.9 | 27.9 |
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 | 2.9 | 11.4 |
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 | 2.9 | 11.4 |
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 | 0.4 | 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 | 0.4 | 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 | 68.2 | 66.6 |
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 | 67.5 | 66.0 |
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 | 0.6 |
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 | 66.7 | 72.9 | 68.2
Assets measured at net asset value | 19.0 | 0.0 |
Total assets in fair value hierarchy | 47.7 | 72.9 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 47.7 | 72.9 |
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 | 0.7 | 0.3 |
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 | 0.7 | 0.3 |
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] | Equity securites - U.S. [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 22.3 |
Other Postretirement Benefit 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 | 0.0 | 22.3 |
Other Postretirement Benefit 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 |
Other Postretirement Benefit 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 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Equity securities - international [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 7.5 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Equity securities - international [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0.0 | 7.5 |
Other Postretirement Benefit 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 |
Other Postretirement Benefit 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 |
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Fixed income securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 47.0 | 42.8 |
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 | 47.0 | 42.8 |
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 | 16.7 | 18.7 | $ 18.6
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 16.7 | 18.4 |
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 | 0.3 |
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 | 0.1 | 0.6 |
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 | 0.1 | 0.3 |
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 | 0.3 |
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 | 16.6 | 18.1 |
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 | 16.6 | 18.1 |
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 | (0.5) | (0.7) |
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 | $ (0.2) | $ (0.3) |

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