Detail of Income Tax Difference From Statutory Rate (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule Of Effective Tax Rates Line Items
Expected income tax expense	$ 10.0	$ 7.5	$ 72.0
Tax difference related to investment disposals and maturities	(14.3)	(9.7)	(3.2)
Change in valuation allowance	(7.7)	(7.5)	(57.1)
Effect of foreign operations	(3.9)	(1.5)
Dividend received deduction	(2.8)	(1.1)	(0.8)
Nondeductible expenses	2.8	4.7	0.5
Expired capital loss carryforward			47.4
Tax-exempt interest	(1.5)	(2.0)	(2.2)
Tax credits		(0.2)	(0.4)
Other, net		(0.1)	(0.2)
Income tax expense (benefit)	$ (17.4)	$ (9.9)	$ 56.0
Effective tax rate	(60.60%)	(45.80%)	27.20%

Income Tax Reconciliation Capital Loss Carryforward

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Income Tax Reconciliation, Effect Of Foreign Operations

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Income Tax Reconciliation, Tax Difference Related To Investment Disposals And Maturities

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A ratio calculated by dividing the reported amount of income tax expense attributable to continuing operations for the period by GAAP-basis pretax income from continuing operations.

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The sum of the current income tax expense or benefit and the deferred income tax expense or benefit pertaining to continuing operations.

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-Glossary Income Tax Expense (or Benefit)

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The portion of the difference between total income tax expense or benefit as reported in the Income Statement and the expected income tax expense or benefit computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations attributable to changes in the valuation allowance for deferred tax assets in the period.

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The portion of the difference between total income tax expense or benefit as reported in the Income Statement for the period and the expected income tax expense or benefit computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations attributable to the deduction for dividends paid or received under enacted tax laws.

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The amount of income tax expense or benefit for the period computed by applying the domestic federal statutory tax rates to pretax income from continuing operations.

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The sum of the differences between total income tax expense or benefit as reported in the Income Statement for the period and the expected income tax expense or benefit computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations attributable to nondeductible expenses under enacted tax laws, or differences in the methodologies used to determine expense amounts for financial statements prepared in accordance with generally accepted accounting principles and enacted tax laws.

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The portion of the difference, between total income tax expense or benefit as reported in the Income Statement for the year/accounting period and the expected income tax expense or benefit computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations, that is attributable to all other items not otherwise listed in the existing taxonomy.

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The portion of the difference between total income tax expense or benefit as reported in the Income Statement for the period and the expected income tax expense or benefit computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations attributable to income that is exempt from income taxes under enacted tax laws.

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