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Benefit Plans (Narrative) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2016 | Dec. 31, 2015
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 | 12.60% | 11.60%
Percentage of employees accepting voluntary separation package |  | 2.00%
Voluntary employee separation charges |  | $ 8.0
Unrecognized compensation cost | $ 5.0 |
Percentage of base salary and performance-based compensation | 100.00% |
Performance Shares and Performance Units [Member] |  |
Benefit Plans [Line Items] |  |
Performance period | 3 years |
Actual number of shares paid out upon vesting, minimum percentage of target shares | 0.00% |
Actual number of shares paid out upon vesting, maximum percentage of target shares | 200.00% |
Performance Shares [Member] |  |
Benefit Plans [Line Items] |  |
Instrument valuation based on shares of common stock, number of shares | 1 |
Performance Units [Member] |  |
Benefit Plans [Line Items] |  |
Instrument valuation based on shares of common stock, number of shares | 1 |
Restricted Stock Units [Member] |  |
Benefit Plans [Line Items] |  |
Performance period | 3 years |
Actual number of shares paid out upon vesting, minimum percentage of target shares | 0.00% |
Actual number of shares paid out upon vesting, maximum percentage of target shares | 200.00% |
Performance Restricted Stock Unit [Member] |  |
Benefit Plans [Line Items] |  |
Instrument valuation based on shares of common stock, number of shares | 1 |
Restricted Stock Unit And Restricted Unit [Member] |  |
Benefit Plans [Line Items] |  |
Performance period | 3 years |
Instrument valuation based on shares of common stock, number of shares | 1 |
Performance Contingent Cash Awards [Member] |  |
Benefit Plans [Line Items] |  |
Instrument valuation based on shares of common stock, number of shares | 1 |
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
Unrecognized compensation cost | $ 2.7 |
WPL [Member] |  |
Benefit Plans [Line Items] |  |
Voluntary employee separation charges |  | $ 3.0
Unrecognized compensation cost | 2.2 |
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 | 7,400,000 |
2016 Grant [Member] | Performance Units [Member] |  |
Benefit Plans [Line Items] |  |
Instrument valuation based on shares of common stock, number of shares | 1 |

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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 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585 Reference 2: 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 3: 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 4: 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=65897934&loc=d3e1928-114920 Reference 5: 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 + Details
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