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Benefit Plans (Defined Benefit Pension And Other Postretirement Benefits Plans) (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2019 | Jun. 30, 2018 | Jun. 30, 2019 | Jun. 30, 2018
Defined benefit pension plans [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Service cost | $ 2.4 | $ 3.0 | $ 4.8 | $ 6.0
Interest cost | 12.4 | 11.7 | 24.9 | 23.4
Expected return on plan assets | (15.0) | (17.5) | (30.0) | (34.9)
Amortization of prior service credit | (0.1) | (0.1) | (0.3) | (0.3)
Amortization of actuarial loss | 9.1 | 8.8 | 18.2 | 17.6
Total | 8.8 | 5.9 | 17.6 | 11.8
OPEB Plans [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Service cost | 0.9 | 1.0 | 1.7 | 2.1
Interest cost | 2.1 | 1.9 | 4.2 | 3.8
Expected return on plan assets | (1.3) | (1.5) | (2.5) | (3.0)
Amortization of prior service credit | (0.1) | (0.1) | (0.1) | (0.1)
Amortization of actuarial loss | 0.8 | 0.9 | 1.6 | 1.7
Total | 2.4 | 2.2 | 4.9 | 4.5
IPL [Member] | Defined benefit pension plans [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Service cost | 1.5 | 1.9 | 3.0 | 3.7
Interest cost | 5.7 | 5.4 | 11.4 | 10.7
Expected return on plan assets | (7.1) | (8.2) | (14.1) | (16.3)
Amortization of prior service credit | 0.0 | (0.1) | (0.1) | (0.1)
Amortization of actuarial loss | 4.0 | 3.8 | 7.9 | 7.5
Total | 4.1 | 2.8 | 8.1 | 5.5
IPL [Member] | OPEB Plans [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Service cost | 0.4 | 0.5 | 0.7 | 0.9
Interest cost | 0.9 | 0.8 | 1.7 | 1.6
Expected return on plan assets | (0.9) | (1.1) | (1.8) | (2.2)
Amortization of prior service credit | 0.0 | 0.0 | 0.0 | 0.0
Amortization of actuarial loss | 0.3 | 0.3 | 0.7 | 0.6
Total | 0.7 | 0.5 | 1.3 | 0.9
WPL [Member] | Defined benefit pension plans [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Service cost | 0.8 | 1.1 | 1.7 | 2.2
Interest cost | 5.4 | 5.1 | 10.8 | 10.1
Expected return on plan assets | (6.6) | (7.6) | (13.1) | (15.2)
Amortization of prior service credit | 0.0 | (0.1) | (0.1) | (0.1)
Amortization of actuarial loss | 4.4 | 4.3 | 8.8 | 8.6
Total | 4.0 | 2.8 | 8.1 | 5.6
WPL [Member] | OPEB Plans [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Service cost | 0.3 | 0.4 | 0.6 | 0.8
Interest cost | 0.9 | 0.7 | 1.7 | 1.5
Expected return on plan assets | (0.2) | (0.1) | (0.3) | (0.3)
Amortization of prior service credit | (0.1) | (0.1) | (0.1) | (0.1)
Amortization of actuarial loss | 0.4 | 0.5 | 0.8 | 1.0
Total | $ 1.3 | $ 1.4 | $ 2.7 | $ 2.9

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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/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(4) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2709-114920 + 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/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(5) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (a)(5) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2709-114920 + 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/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(3) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2709-114920 + 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/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(2) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2709-114920 + Details
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