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Benefit Plans (Narrative) (Details) - USD ($) shares in Millions, $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2015 | Dec. 31, 2014
Benefit Plans [Line Items] |  |
Total plan assets, percentage of common stock (less than 1%) | 1.00% | 1.00%
Common stock percentage in assets held in 401(k) saving plans | 11.60% | 12.60%
Percentage of employees accepting voluntary separation package | 2.00% |
Voluntary employee separation charges | $ 8.0 |
Unrecognized compensation cost | $ 3.9 |
Percentage of base salary and performance-based compensation | 100.00% |
Performance Shares and Units [Member] |  |
Benefit Plans [Line Items] |  |
Performance period | 3 years |
Performance Units [Member] |  |
Benefit Plans [Line Items] |  |
Performance multiplier range, lower | 0.00% |
Performance multiplier range, upper | 200.00% |
Minimum [Member] |  |
Benefit Plans [Line Items] |  |
Unrecognized compensation cost recognized over a weighted average period | 1 year |
Minimum [Member] | Performance-Contingent Restricted Stock [Member] |  |
Benefit Plans [Line Items] |  |
Performance period | 2 years |
Minimum [Member] | Performance Contingent Cash Awards [Member] |  |
Benefit Plans [Line Items] |  |
Performance period | 2 years |
Maximum [Member] |  |
Benefit Plans [Line Items] |  |
Unrecognized compensation cost recognized over a weighted average period | 2 years |
Maximum [Member] | Performance-Contingent Restricted Stock [Member] |  |
Benefit Plans [Line Items] |  |
Performance period | 4 years |
Maximum [Member] | Performance Contingent Cash Awards [Member] |  |
Benefit Plans [Line Items] |  |
Performance period | 4 years |
IPL [Member] |  |
Benefit Plans [Line Items] |  |
Voluntary employee separation charges | $ 5.0 |
WPL [Member] |  |
Benefit Plans [Line Items] |  |
Voluntary employee separation charges | 3.0 |
Other Postretirement Benefits Plans [Member] |  |
Benefit Plans [Line Items] |  |
Plan asset threshold for long-term allocation targets | 5.0 |
Other Postretirement Benefits Plans [Member] | IPL [Member] |  |
Benefit Plans [Line Items] |  |
Plan asset threshold for long-term allocation targets | 5.0 |
Other Postretirement Benefits Plans [Member] | WPL [Member] |  |
Benefit Plans [Line Items] |  |
Plan asset threshold for long-term allocation targets | $ 5.0 |
Omnibus Incentive Plan [Member] |  |
Benefit Plans [Line Items] |  |
Shares available for issuance under the Amended and Restated OIP | 3.8 |

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- Definition Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Amount of expenses for special or contractual termination benefits provided to current employees involuntarily terminated under a benefit arrangement associated exit or disposal activities pursuant to an authorized plan. Excludes expenses related to one-time termination benefits, a discontinued operation or an asset retirement obligation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SAB TOPIC 5.P.4(b)) -URI http://asc.fasb.org/extlink&oid=27011515&loc=d3e140904-122747 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 5.P.3) -URI http://asc.fasb.org/extlink&oid=27011515&loc=d3e140864-122747 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(10) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 5 -Section P -Subsection 3, 4 + Details
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- Definition The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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