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Income Taxes (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Summary of income tax expense |  |  |
Current tax expense (benefit) | $ 72.7 | $ 15.1 | $ 33.6
Deferred income taxes | 498.7 | 420.4 | 329.2
Investment tax credit, net | (4.9) | (1.7) | (1.1)
Total income tax expense, amount | 566.5 | 433.8 | 361.7
Reconciliation of the beginning and ending amount of unrecognized tax benefits |  |  |
Balance, January 1 | 9.5 | 7.2 |
Acquired legacy Integrys tax assets | 0.0 | (3.6) |
Additions for tax positions of prior years | 6.7 | 0.3 |
Additions based on tax positions related to the current year | 1.1 | 0.2 |
Reductions for tax positions of prior years | (1.0) | (1.1) |
Reductions due to statute of limitations | (1.8) | 0.0 |
Settlements during the period | 0.0 | (0.7) |
Balance, December 31 | 14.5 | 9.5 | 7.2
Income Taxes |  |  |
Deferred tax assets, uncertainty in income taxes | 6.6 | 6.2 |
Net amount of unrecognized tax benefits having impact on the effective tax rate for continuing operations | 7.9 | 2.2 |
Accrued interest in the consolidated income statements | 0.2 | 0.0 | 0.3
Accrued penalties in the consolidated income statements | 0.0 | 0.0 | $ 0.0
Accrued interest on the consolidated balance sheets | 0.8 | 0.7 |
Accrued penalties on the consolidated balance sheets | $ 0.0 | $ 0.1 |

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- Definition The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=65882285&loc=SL6600010-109319 + Details
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