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Employee Share-Based Incentive Compensation Plans (WTM Phantom Performance Shares Granted Under WTM Phantom Shares Plan) (Details) (USD $) In Millions, except Share data, unless otherwise specified | Dec. 31, 2012 | Dec. 31, 2011
--- | --- | ---
Share-based compensation arrangement by share-based payment award |  |  |
Accrued incentive compensation | $ 159.0 |  | $ 187.9
Performance Share | W T M Phantom Share Plans |  |  |
Share-based compensation arrangement by share-based payment award |  |  |
Options nonvested, number before forfeitures (in shares) | 4,990 |  |
Incentive compensation payable before forfeitures | 2.6 |  |
Assumed rorfeitures in period (in shares) | (125) |  |
Assumed forfeitures in period amount | 0 |  |
Shares outstanding (in shares) | 4,865 |  |
Accrued incentive compensation | 2.6 |  |
Performance Share | Performance Cycle From 2010 to 2012 | W T M Phantom Share Plans |  |  |
Share-based compensation arrangement by share-based payment award |  |  |
Options nonvested, number before forfeitures (in shares) | 4,990 |  |
Incentive compensation payable before forfeitures | 2.6 |  |
Performance Share | Performance Cycle From 2011 to 2013 | W T M Phantom Share Plans |  |  |
Share-based compensation arrangement by share-based payment award |  |  |
Options nonvested, number before forfeitures (in shares) | 0 | [1] |
Incentive compensation payable before forfeitures | 0 | [1] |
Performance Share | Performance Cycle From 2012 to 2014 | W T M Phantom Share Plans |  |  |
Share-based compensation arrangement by share-based payment award |  |  |
Options nonvested, number before forfeitures (in shares) | 0 | [1] |
Incentive compensation payable before forfeitures | 0 | [1] |
W T M Incentive Plan | Performance Share |  |  |
Share-based compensation arrangement by share-based payment award |  |  |
Options nonvested, number before forfeitures (in shares) | 117,427 |  |
Incentive compensation payable before forfeitures | 27.6 |  |
Assumed rorfeitures in period (in shares) | (2,935) |  |
Assumed forfeitures in period amount | 0.8 |  |
Shares outstanding (in shares) | 114,492 |  |
Accrued incentive compensation | 26.8 |  |
W T M Incentive Plan | Performance Cycle From 2010 to 2012 | Performance Share |  |  |
Share-based compensation arrangement by share-based payment award |  |  |
Options nonvested, number before forfeitures (in shares) | 42,320 |  |
Incentive compensation payable before forfeitures | 7.3 |  |
W T M Incentive Plan | Performance Cycle From 2011 to 2013 | Performance Share |  |  |
Share-based compensation arrangement by share-based payment award |  |  |
Options nonvested, number before forfeitures (in shares) | 37,130 |  |
Incentive compensation payable before forfeitures | 12.7 |  |
W T M Incentive Plan | Performance Cycle From 2012 to 2014 | Performance Share |  |  |
Share-based compensation arrangement by share-based payment award |  |  |
Options nonvested, number before forfeitures (in shares) | 37,977 |  |
Incentive compensation payable before forfeitures | $ 7.6 |  |
[1] | All performance shares for the 2011–2013 and 2012–2014 performance cycles were granted from the WTM Incentive Plan.

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- Definition The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date. + 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 (c)(2)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 123R -Paragraph A240 -Subparagraph b(2)(b) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 123R -Paragraph A240 -Subparagraph b(2)(a) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
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- Details
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- Definition Aggregate carrying value as of the balance sheet date of liabilities for incentive compensation arrangements. + References No definition available. + Details
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Balance Type: | credit
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- Definition Carrying value as of the balance sheet date for performance shares before forfeitures. + References No definition available. + Details
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- Definition This element represents the reduction for assumed forfeitures to the number of performance shares outstanding. + References No definition available. + Details
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- Definition This element represents the reduction to accrued expense for assumed forfeitures of performance shares. + References No definition available. + Details
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- Definition This element represents the number of non-vested performance shares before forfeiture assumptions. + References No definition available. + Details
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