XML 146 R130.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Financial Statement Revisions - Statement of Shareholders' Equity (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Error Corrections and Prior Period Adjustments Restatement [Line Items] |  |  |  |
Beginning balance | $ 3,716.0 |  |  |
Repurchases and retirements of common shares | (723.9) | $ (887.2) | $ (284.2) |
Net income | 593.1 | 409.0 | 276.7 |
Ending balance | 3,360.8 | 3,716.0 |  |
Previously Reported |  |  |  |
Error Corrections and Prior Period Adjustments Restatement [Line Items] |  |  |  |
Beginning balance | 3,737.2 |  |  |
Net income |  | 419.8 | 279.5 |
Ending balance |  | 3,737.2 |  |
Adjustment |  |  |  |
Error Corrections and Prior Period Adjustments Restatement [Line Items] |  |  |  |
Beginning balance | (21.2) |  |  |
Net income |  | (10.8) | (2.8) |
Ending balance |  | (21.2) |  |
Common shares and paid-in surplus |  |  |  |
Error Corrections and Prior Period Adjustments Restatement [Line Items] |  |  |  |
Beginning balance | 810.7 | 978.2 | 1,034.7 |
Repurchases and retirements of common shares | (147.9) | (192.4) | (67.0) |
Ending balance |  | 810.7 | 978.2 | $ 1,034.7
Common shares and paid-in surplus | Previously Reported |  |  |  |
Error Corrections and Prior Period Adjustments Restatement [Line Items] |  |  |  |
Beginning balance | 810.7 | 978.2 | 1,034.7 |
Ending balance |  | 810.7 | 978.2 | 1,034.7
Common shares and paid-in surplus | Adjustment |  |  |  |
Error Corrections and Prior Period Adjustments Restatement [Line Items] |  |  |  |
Beginning balance | 0.0 | 0.0 | 0.0 |
Ending balance |  | 0.0 | 0.0 | 0.0
Retained earnings |  |  |  |
Error Corrections and Prior Period Adjustments Restatement [Line Items] |  |  |  |
Beginning balance | 2,776.6 | 3,075.0 | 3,003.0 | 2,801.4
Repurchases and retirements of common shares | (576.0) | (694.8) | (217.2) | (97.4)
Net income | 627.2 | 401.8 | 295.2 | 305.2
Dividends declared on common shares | (4.6) | (5.4) | (6.0) | (6.2)
Net other changes in AOCI |  | 113.9 | (34.6) | 66.6
Ending balance |  | 2,776.6 | 3,075.0 | 3,003.0
Retained earnings | Previously Reported |  |  |  |
Error Corrections and Prior Period Adjustments Restatement [Line Items] |  |  |  |
Beginning balance | 2,797.2 | 3,084.9 | 3,010.5 | 2,801.9
Repurchases and retirements of common shares |  | (694.8) | (217.2) | (97.4)
Net income |  | 412.5 | 297.6 | 312.2
Dividends declared on common shares |  | (5.4) | (6.0) | (6.2)
Net other changes in AOCI |  | 113.9 | (34.6) | 66.6
Ending balance |  | 2,797.2 | 3,084.9 | 3,010.5
Retained earnings | Adjustment |  |  |  |
Error Corrections and Prior Period Adjustments Restatement [Line Items] |  |  |  |
Beginning balance | (20.6) | (9.9) | (7.5) | (0.5)
Repurchases and retirements of common shares |  | 0.0 | 0.0 | 0.0
Net income |  | (10.7) | (2.4) | (7.0)
Dividends declared on common shares |  | 0.0 | 0.0 | 0.0
Net other changes in AOCI |  | 0.0 | 0.0 | 0.0
Ending balance |  | (20.6) | (9.9) | (7.5)
AOCL, after-tax |  |  |  |
Error Corrections and Prior Period Adjustments Restatement [Line Items] |  |  |  |
Beginning balance | (4.6) | (149.9) | (42.1) | 52.6
Ending balance |  | (4.6) | (149.9) | (42.1)
AOCL, after-tax | Previously Reported |  |  |  |
Error Corrections and Prior Period Adjustments Restatement [Line Items] |  |  |  |
Beginning balance | (4.6) | (149.9) | (49.5) | 52.1
Net change in pension liability and other accumulated comprehensive items |  | 31.4 | (65.8) | (168.2)
Ending balance |  | (4.6) | (149.9) | (49.5)
AOCL, after-tax | Adjustment |  |  |  |
Error Corrections and Prior Period Adjustments Restatement [Line Items] |  |  |  |
Beginning balance | 0.0 | 0.0 | 7.4 | 0.5
Ending balance |  | 0.0 | 0.0 | 7.4
Parent |  |  |  |
Error Corrections and Prior Period Adjustments Restatement [Line Items] |  |  |  |
Beginning balance | 3,582.7 | 3,903.3 | 3,995.6 |
Repurchases and retirements of common shares | (723.9) | (887.2) | (284.2) |
Net income | 627.2 | 401.8 | 295.2 |
Dividends declared on common shares | (4.6) | (5.4) | (6.0) |
Ending balance |  | 3,582.7 | 3,903.3 | 3,995.6
Parent | Previously Reported |  |  |  |
Error Corrections and Prior Period Adjustments Restatement [Line Items] |  |  |  |
Beginning balance | 3,603.3 | 3,913.2 | 3,995.7 |
Ending balance |  | 3,603.3 | 3,913.2 | 3,995.7
Parent | Adjustment |  |  |  |
Error Corrections and Prior Period Adjustments Restatement [Line Items] |  |  |  |
Beginning balance | (20.6) | (9.9) | (0.1) |
Ending balance |  | (20.6) | (9.9) | (0.1)
Non-controlling interests |  |  |  |
Error Corrections and Prior Period Adjustments Restatement [Line Items] |  |  |  |
Beginning balance | 133.3 | 454.3 | 542.6 | 491.7
Repurchases and retirements of common shares | (5.2) |  |  |
Net income | (34.1) | 7.2 | (18.5) | (22.3)
Other changes in NCI |  | (328.2) | (69.8) | 73.2
Ending balance |  | 133.3 | 454.3 | 542.6
Non-controlling interests | Previously Reported |  |  |  |
Error Corrections and Prior Period Adjustments Restatement [Line Items] |  |  |  |
Beginning balance | 133.9 | 454.8 | 542.7 | 491.7
Net income |  | 7.3 | (18.1) | (22.2)
Other changes in NCI |  | (328.2) | (69.8) | 73.2
Ending balance |  | 133.9 | 454.8 | 542.7
Non-controlling interests | Adjustment |  |  |  |
Error Corrections and Prior Period Adjustments Restatement [Line Items] |  |  |  |
Beginning balance | (0.6) | (0.5) | (0.1) | 0.0
Net income |  | (0.1) | (0.4) | (0.1)
Other changes in NCI |  | 0.0 | 0.0 | 0.0
Ending balance |  | (0.6) | (0.5) | (0.1)
Total equity |  |  |  |
Error Corrections and Prior Period Adjustments Restatement [Line Items] |  |  |  |
Beginning balance | 3,716.0 | 4,357.6 | 4,538.2 |
Repurchases and retirements of common shares | (729.1) | (887.2) | (284.2) |
Net income | 593.1 | 409.0 | 276.7 |
Dividends declared on common shares | (4.6) | (5.4) | (6.0) |
Ending balance |  | 3,716.0 | 4,357.6 | 4,538.2
Total equity | Previously Reported |  |  |  |
Error Corrections and Prior Period Adjustments Restatement [Line Items] |  |  |  |
Beginning balance | 3,737.2 | 4,368.0 | 4,538.4 |
Ending balance |  | 3,737.2 | 4,368.0 | 4,538.4
Total equity | Adjustment |  |  |  |
Error Corrections and Prior Period Adjustments Restatement [Line Items] |  |  |  |
Beginning balance | (21.2) | (10.4) | (0.2) |
Ending balance |  | (21.2) | (10.4) | (0.2)
Foreign Currency Gain (Loss) | AOCL, after-tax |  |  |  |
Error Corrections and Prior Period Adjustments Restatement [Line Items] |  |  |  |
Net change in pension liability and other accumulated comprehensive items | 0.4 | 31.4 | (73.2) | (161.3)
Foreign Currency Gain (Loss) | AOCL, after-tax | Adjustment |  |  |  |
Error Corrections and Prior Period Adjustments Restatement [Line Items] |  |  |  |
Net change in pension liability and other accumulated comprehensive items |  | 0.0 | (7.4) | $ 6.9
Foreign Currency Gain (Loss) | Parent |  |  |  |
Error Corrections and Prior Period Adjustments Restatement [Line Items] |  |  |  |
Net change in pension liability and other accumulated comprehensive items | 0.4 | 31.4 | (73.2) |
Foreign Currency Gain (Loss) | Non-controlling interests |  |  |  |
Error Corrections and Prior Period Adjustments Restatement [Line Items] |  |  |  |
Net change in pension liability and other accumulated comprehensive items | 0.1 | 0.3 |  |
Foreign Currency Gain (Loss) | Total equity |  |  |  |
Error Corrections and Prior Period Adjustments Restatement [Line Items] |  |  |  |
Net change in pension liability and other accumulated comprehensive items | $ 0.5 | $ 31.7 | $ (73.2) |

X
- Definition Amount of paid and unpaid common stock dividends declared with the form of settlement in cash. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 + Details
Name: | us-gaap_DividendsCommonStockCash
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- 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
Name: | us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount after tax and reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 830 -SubTopic 30 -Section 45 -Paragraph 20 -Subparagraph (b,c) -URI http://asc.fasb.org/extlink&oid=64808268&loc=d3e32211-110900 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669646-108580 + Details
Name: | us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 55 -Paragraph 4K -URI http://asc.fasb.org/extlink&oid=84234705&loc=SL4591552-111686 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 45 -Paragraph 19 -URI http://asc.fasb.org/extlink&oid=96868048&loc=SL4569616-111683 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 1A -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=84161450&loc=SL4573702-111684 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 55 -Paragraph 4J -URI http://asc.fasb.org/extlink&oid=84234705&loc=SL4591551-111686 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 1A -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=84161450&loc=SL4573702-111684 + Details
Name: | us-gaap_ProfitLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount after tax of reclassification adjustments of other comprehensive income (loss) attributable to parent. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669686-108580 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 55 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=84158357&loc=d3e1436-108581 + Details
Name: | us-gaap_ReclassificationFromAociCurrentPeriodNetOfTaxAttributableToParent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Equity impact of the value of stock that has been repurchased and retired during the period. The excess of the purchase price over par value can be charged against retained earnings (once the excess is fully allocated to additional paid in capital). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21463-112644 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(28)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(29)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 + Details
Name: | us-gaap_StockRepurchasedAndRetiredDuringPeriodValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of stockholders' equity (deficit), net of receivables from officers, directors, owners, and affiliates of the entity, attributable to both the parent and noncontrolling interests. Amount excludes temporary equity. Alternate caption for the concept is permanent equity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 55 -Paragraph 4I -URI http://asc.fasb.org/extlink&oid=84234705&loc=SL4590271-111686 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 45 -Paragraph 16 -URI http://asc.fasb.org/extlink&oid=96868048&loc=SL4568740-111683 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 45 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=96868048&loc=SL4568447-111683 + Details
Name: | us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition This element represents movements included in the statement of changes in stockholders' equity which are not separately disclosed or provided for elsewhere in the taxonomy. + References No definition available. + Details
Name: | us-gaap_StockholdersEquityOther
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_StatementScenarioAxis=us-gaap_ScenarioPreviouslyReportedMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementScenarioAxis=us-gaap_ScenarioAdjustmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementEquityComponentsAxis=us-gaap_CommonStockIncludingAdditionalPaidInCapitalMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementEquityComponentsAxis=us-gaap_RetainedEarningsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementEquityComponentsAxis=us-gaap_AccumulatedOtherComprehensiveIncomeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementEquityComponentsAxis=us-gaap_ParentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementEquityComponentsAxis=us-gaap_NoncontrollingInterestMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementEquityComponentsAxis=wtm_TotalEquityIncludesNoncontrollingInterestMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_OtherComprehensiveIncomeLocationAxis=us-gaap_ForeignCurrencyGainLossMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |