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Benefit Plans (Assumptions Used To Measure Benefit Plans) (Details) | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Pension Plans, Defined Benefit [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate for benefit obligations | 3.66% | 4.19% | 4.47%
Discount rate for net periodic cost | 4.19% | 4.47% | 4.18%
Expected rate of return on plan assets | 7.60% | 7.60% | 7.60%
Pension Plans, Defined Benefit [Member] | IPL [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate for benefit obligations | 3.68% | 4.22% | 4.50%
Discount rate for net periodic cost | 4.22% | 4.50% | 4.20%
Expected rate of return on plan assets | 7.60% | 7.60% | 7.60%
Rate of compensation increase | 3.65% | 3.65% | 3.65%
Pension Plans, Defined Benefit [Member] | WPL [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate for benefit obligations | 3.69% | 4.23% | 4.51%
Discount rate for net periodic cost | 4.23% | 4.51% | 4.20%
Expected rate of return on plan assets | 7.60% | 7.60% | 7.60%
Rate of compensation increase | 3.65% | 3.65% | 3.65%
Other Postretirement Benefits Plans [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate for benefit obligations | 3.53% | 3.98% | 4.30%
Discount rate for net periodic cost | 3.98% | 4.30% | 3.97%
Expected rate of return on plan assets | 5.80% | 6.30% | 6.20%
Medical cost trend on covered charges, initial trend rate (end of year) | 6.75% | 7.00% | 7.25%
Medical cost trend on covered charges, ultimate trend rate | 5.00% | 5.00% | 5.00%
Other Postretirement Benefits Plans [Member] | IPL [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate for benefit obligations | 3.51% | 3.95% | 4.28%
Discount rate for net periodic cost | 3.95% | 4.28% | 3.94%
Expected rate of return on plan assets | 6.20% | 6.60% | 6.60%
Medical cost trend on covered charges, initial trend rate (end of year) | 6.75% | 7.00% | 7.25%
Medical cost trend on covered charges, ultimate trend rate | 5.00% | 5.00% | 5.00%
Other Postretirement Benefits Plans [Member] | WPL [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate for benefit obligations | 3.51% | 3.96% | 4.28%
Discount rate for net periodic cost | 3.96% | 4.28% | 3.96%
Expected rate of return on plan assets | 3.50% | 4.70% | 4.60%
Medical cost trend on covered charges, initial trend rate (end of year) | 6.75% | 7.00% | 7.25%
Medical cost trend on covered charges, ultimate trend rate | 5.00% | 5.00% | 5.00%
Minimum [Member] | Pension Plans, Defined Benefit [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Rate of compensation increase | 3.65% | 3.65% | 3.65%
Maximum [Member] | Pension Plans, Defined Benefit [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Rate of compensation increase | 4.50% | 4.50% | 4.50%

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- Definition The interest rate used to adjust for the time value of money for the 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 (k)(1) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920 + Details
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- Definition Expected rate of compensation increases (for pay-related plans). + 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 (k)(2) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920 + Details
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- Definition The interest rate used to adjust for the time value of money. + 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 (k)(1) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920 + Details
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- Definition An assumption as to the rate of return on plan assets reflecting the average rate of earnings expected on the funds invested or to be invested to provide for the benefits included in the benefit obligation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Expected Long-Term Rate of Return on Plan Assets -URI http://asc.fasb.org/extlink&oid=6512046 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(3) -URI http://asc.fasb.org/extlink&oid=65897934&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 The assumed health care cost trend rate for the next year used to measure the expected cost of benefits covered by the plan (gross eligible charges). This is based upon the annual rate of change in the cost of health care benefits currently provided by the postretirement benefit plan, due to factors other than changes in the composition of the plan population by age and dependency status. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Health Care Cost Trend Rate -URI http://asc.fasb.org/extlink&oid=6514820 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (l) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920 + Details
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- Definition The ultimate trend rate for health care costs. + 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 (l) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920 + Details
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