Income Taxes - Income Tax Reconciliation (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Disclosure [Abstract]
Income (loss) before income taxes	$ 490.5	$ 516.6	$ 315.3
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Tax rate	35.00%	35.00%	35.00%
Income tax expense (benefit) at federal statutory rate	171.7	180.8	110.4
Dividends received deduction	(26.6)	(18.6)	(37.0)
Valuation allowance	67.6	0	(87.0)
Audit settlements	(0.3)	(0.3)	3.7
Prior year tax	0	28.1	0
Other	(5.4)	1.2	4.9
Income tax expense (benefit)	$ 207.0	$ 191.2	$ (5.0)

Income Tax Reconciliation, Deductions, Audit Settlement

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Sum of operating profit and nonoperating income or expense before Income or Loss from equity method investments, income taxes, extraordinary items, and noncontrolling interest.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to increase (decrease) in the valuation allowance for deferred tax assets.

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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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Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to revisions of previously reported income tax expense (benefit).

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