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Income Taxes (Tables) | 12 Months Ended
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Dec. 31, 2017
Income Tax Disclosure [Abstract] |
Schedule of total income tax benefit (expense) | The following table presents the total income tax benefit for the years ended December 31, 2017, 2016 and 2015:
|  | Year Ended December 31,
Millions |  | 2017 |  | 2016 |  | 2015
Current tax (expense) benefit: |  |  |  |  |  |  |  |  |
U.S. federal |  | $ | (.3 | ) |  | $ | 21.4 |  |  | $ | — |
State |  | (1.3 | ) |  | (.7 | ) |  | (.6 | )
Non-U.S. |  | (2.0 | ) |  | (.3 | ) |  | (.8 | )
Total current tax (expense) benefit |  | (3.6 | ) |  | 20.4 |  |  | (1.4 | )
Deferred tax benefit (expense): |  |  |  |  |  |  |  |  |
U.S. federal |  | 11.4 |  |  | 12.5 |  |  | (11.3 | )
Total deferred tax benefit (expense) |  | 11.4 |  |  | 12.5 |  |  | (11.3 | )
Total income tax benefit (expense) |  | $ | 7.8 |  |  | $ | 32.9 |  |  | $ | (12.7 | )
Reconciliation of the U.S. federal statutory income tax rate and actual effective tax rate on pre-tax income | The following table presents a reconciliation of taxes calculated using the 35% U.S. statutory rate (the tax rate at which the majority of White Mountains’s worldwide operations are taxed) to the income tax (expense) benefit on pre-tax income:
|  | Year Ended December 31,
Millions |  | 2017 |  | 2016 |  | 2015
Tax (expense) benefit at the U.S. statutory rate |  | $ | (2.7 | ) |  | $ | 51.6 |  |  | $ | (45.2 | )
Differences in taxes resulting from: |  |  |  |  |  |  |  |  |
Tax rate changes |  | (44.3 | ) |  | (3.9 | ) |  | (.5 | )
Change in valuation allowance |  | 42.6 |  |  | 6.9 |  |  | (21.8 | )
Non-U.S. earnings, net of foreign taxes |  | 21.5 |  |  | (19.2 | ) |  | 58.5 |
Officer compensation |  | (4.1 | ) |  | — |  |  | — |
Member surplus contributions |  | (3.0 | ) |  | (2.3 | ) |  | (1.5 | )
Withholding tax |  | (2.0 | ) |  | (.2 | ) |  | (.5 | )
Tax exempt interest and dividends |  | .5 |  |  | .1 |  |  | — |
Tax reserve adjustments |  | (.3 | ) |  | — |  |  | — |
Other, net |  | (.4 | ) |  | (.1 | ) |  | (1.7 | )
Total income tax benefit (expense) on pre-tax income (loss) |  | $ | 7.8 |  |  | $ | 32.9 |  |  | $ | (12.7 | )
Schedule of components of deferred income tax assets and liabilities | The following table presents an outline of the significant components of White Mountains’s U.S. federal, state (net of federal benefit) and non-U.S. deferred tax assets and liabilities:
|  | December 31,
Millions |  | 2017 |  | 2016
Deferred income tax assets related to: |  |  |  |  |  |
U.S. federal and state net operating and capital loss carryforwards |  | $ | 73.0 |  |  | $ | 104.3 |
Non-U.S. net operating loss carryforwards |  | 33.9 |  |  | 34.0 |
Incentive compensation |  | 20.4 |  |  | 26.5 |
Investment basis difference |  | 4.9 |  |  | 5.6 |
Other items |  | 4.9 |  |  | 8.5 |
Total gross deferred income tax assets |  | 137.1 |  |  | 178.9 |
Less: valuation allowances |  | 109.6 |  |  | 146.2 |
Total net deferred income tax assets |  | 27.5 |  |  | 32.7 |
Deferred income tax liabilities related to: |  |  |  |  |  |
Member surplus contributions |  | 24.1 |  |  | 30.0 |
Other items |  | 2.1 |  |  | 2.7 |
Total deferred income tax liabilities |  | 26.2 |  |  | 32.7 |
Net deferred tax asset |  | $ | 1.3 |  |  | $ | — |
Schedule of net operating and capital loss carryforwards by expiration dates and the deferred tax assets thereon | The following table presents net operating loss and capital loss carryforwards as of December 31, 2017, the expiration dates and the deferred tax assets thereon:
|  | December 31, 2017
Millions |  | United States |  | Luxembourg |  | United Kingdom |  | Israel |  | Total
2018-2022 |  | $ | .3 |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | .3 |
2023-2027 |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
2028-2037 |  | 332.0 |  |  | 46.4 |  |  | — |  |  | — |  |  | 378.4 |
No expiration date |  | — |  |  | 31.3 |  |  | 6.7 |  |  | 54.7 |  |  | 92.7 |
Total |  | $ | 332.3 |  |  | $ | 77.7 |  |  | $ | 6.7 |  |  | $ | 54.7 |  |  | $ | 471.4 |
Gross deferred tax asset |  | 73.0 |  |  | 20.2 |  |  | 1.1 |  |  | 12.6 |  |  | 106.9 |
Valuation allowance |  | (73.0 | ) |  | (20.2 | ) |  | (1.1 | ) |  | (12.6 | ) |  | (106.9 | )
Net deferred tax asset |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |
Reconciliation of changes in the amount of unrecognized tax benefits | The following table presents a reconciliation of the beginning and ending amount of unrecognized tax benefits for 2017:
Millions |  | Permanent Differences (1) |  | Temporary Differences (2) |  | Interest and Penalties (3) |  | Total
Balance at January 1, 2017 |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |
Changes in prior year tax positions |  | .1 |  |  | — |  |  | — |  |  | .1 |
Tax positions taken during the current year |  | .2 |  |  | — |  |  | — |  |  | .2 |
Balance at December 31, 2017 |  | $ | .3 |  |  | $ | — |  |  | $ | — |  |  | $ | .3 |
(1) | Represents the amount of unrecognized tax benefits that, if recognized, would impact the effective tax rate.
(2) | Represents the amount of unrecognized tax benefits that, if recognized, would create a temporary difference between the reported amount of an item in White Mountains’s Consolidated Balance Sheet and its tax basis.
(3) | Net of tax benefit.

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- Definition Tabular disclosure for tax positions taken in the tax returns filed or to be filed for which it is more likely than not that the tax position will not be sustained upon examination by taxing authorities and other income tax contingencies. Includes, but is not limited to, interest and penalties, reconciliation of unrecognized tax benefits, unrecognized tax benefits that would affect the effective tax rate, tax years that remain subject to examination by tax jurisdictions, and information about positions for which it is reasonably possible that amounts unrecognized will significantly change within 12 months. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32718-109319 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 19 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32840-109319 + Details
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