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Benefit Plans (Defined Benefit Pension And Other Postretirement Benefits Plans) (Details) - USD ($) $ in Millions | 3 Months Ended
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Mar. 31, 2018 | Mar. 31, 2017
Defined benefit pension plans [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Service cost | $ 3.0 | $ 3.1
Interest cost | 11.7 | 12.8
Expected return on plan assets | (17.4) | (16.4)
Amortization of prior service credit | (0.2) | (0.1)
Amortization of actuarial loss | 8.8 | 9.4
Total | 5.9 | 8.8
OPEB Plans [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Service cost | 1.1 | 1.2
Interest cost | 1.9 | 2.2
Expected return on plan assets | (1.5) | (1.5)
Amortization of prior service credit | 0.0 | (0.1)
Amortization of actuarial loss | 0.8 | 1.0
Total | 2.3 | 2.8
IPL [Member] | Defined benefit pension plans [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Service cost | 1.8 | 1.8
Interest cost | 5.3 | 5.9
Expected return on plan assets | (8.1) | (7.7)
Amortization of actuarial loss | 3.7 | 4.0
Total | 2.7 | 4.0
IPL [Member] | OPEB Plans [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Service cost | 0.4 | 0.5
Interest cost | 0.8 | 0.9
Expected return on plan assets | (1.1) | (1.1)
Amortization of actuarial loss | 0.3 | 0.5
Total | 0.4 | 0.8
WPL [Member] | Defined benefit pension plans [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Service cost | 1.1 | 1.2
Interest cost | 5.0 | 5.5
Expected return on plan assets | (7.6) | (7.1)
Amortization of prior service credit | 0.0 | 0.0
Amortization of actuarial loss | 4.3 | 4.6
Total | 2.8 | 4.2
WPL [Member] | OPEB Plans [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Service cost | 0.4 | 0.5
Interest cost | 0.8 | 0.9
Expected return on plan assets | (0.2) | (0.2)
Amortization of prior service credit | 0.0 | (0.1)
Amortization of actuarial loss | 0.5 | 0.4
Total | $ 1.5 | $ 1.5

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- Definition Amount of gain (loss) recognized in net periodic benefit (cost) credit of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(4) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Amount of prior service cost (credit) recognized in net periodic benefit cost (credit) of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(5) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition Amount of expected return (loss) recognized in net periodic benefit (cost) credit, calculated based on expected long-term rate of return and market-related value of plan assets of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(3) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Amount of cost recognized for passage of time related to defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(2) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Amount of net periodic benefit cost (credit) for defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Amount of cost for actuarial present value of benefits attributed to service rendered by employee for defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(1) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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