Segments - Operating Earnings Before Income Taxes (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended	12 Months Ended
Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting Information [Line Items]
Total operating earnings before income taxes	$ 528.7	$ 438.6	$ 918.3	$ 1,119.6	$ 620.6
Closed Block Variable Annuity	(815.5)	(525.8)	(692.3)	(564.5)	(220.2)
Net investment gains (losses) and related charges and adjustments	42.6	192.9	455.5	71.8	(96.4)
Net guaranteed benefit hedging gains (losses) and related charges and adjustments	35.5	93.3	97.2	(269.4)	(30.0)
Loss related to businesses exited through reinsurance or divestment	(33.9)	(24.2)	(45.8)	(35.1)	(3.3)
Income (loss) attributable to noncontrolling interests	(16.6)	202.1	138.2	190.9	(10.3)
Loss on early extinguishment of debt			0	0	(108.3)
Immediate recognition of net actuarial gains (losses) related to pension and other post-employment benefit obligations and gains (losses) from plan amendments and curtailments			(165.0)	(157.8)	(47.5)
Other adjustments to operating earnings	(30.3)	(36.7)	(100.1)	(77.7)	(66.8)
Income (loss) before income taxes	(289.5)	340.2	606.0	277.8	37.8
Investment Management
Segment Reporting Information [Line Items]
Total operating earnings before income taxes	71.2	64.2	134.5	87.5	50.1
Total Ongoing Businesses
Segment Reporting Information [Line Items]
Total operating earnings before income taxes	592.2	455.6	990.9	1,279.6	1,030.2
Corporate
Segment Reporting Information [Line Items]
Total operating earnings before income taxes	(102.9)	(81.1)	(182.3)	(230.2)	(399.1)
Closed Blocks
Segment Reporting Information [Line Items]
Total operating earnings before income taxes	39.4	64.1	109.7	70.2	(10.5)
Retirement \| Retirement Solutions
Segment Reporting Information [Line Items]
Total operating earnings before income taxes	269.9	195.0	448.6	441.9	469.6
Annuities \| Retirement Solutions
Segment Reporting Information [Line Items]
Total operating earnings before income taxes	113.8	63.3	102.2	387.6	115.0
Individual Life \| Insurance Solutions
Segment Reporting Information [Line Items]
Total operating earnings before income taxes	90.8	88.4	196.2	279.3	313.5
Employee Benefits \| Insurance Solutions
Segment Reporting Information [Line Items]
Total operating earnings before income taxes	46.5	44.7	109.4	83.3	82.0
Closed Block Institutional Spread Products \| Closed Blocks
Segment Reporting Information [Line Items]
Total operating earnings before income taxes	33.0	31.0	45.7	83.2	(3.8)
Closed Block Other \| Closed Blocks
Segment Reporting Information [Line Items]
Total operating earnings before income taxes	$ 6.4	$ 33.1	$ 64.0	$ (13.0)	$ (6.7)

Amount of gain (loss) related to change in benefit obligation resulting from changes in actuarial assumptions, for example, but not limited to, interest, mortality, employee turnover, salary, and temporary deviation from the substantive plan.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 30

-Glossary Gain or Loss

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Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects.

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This item represents the net total realized and unrealized gain (loss) included in earnings for the period as a result of selling or holding marketable securities categorized as trading, available-for-sale, or held-to-maturity, including the unrealized holding gain (loss) of held-to-maturity securities transferred to the trading security category and the cumulative unrealized gain (loss) which was included in other comprehensive income (a separate component of shareholders' equity) for available-for-sale securities transferred to trading securities during the period. Additionally, this item would include any gains (losses) realized during the period from the sale of investments accounted for under the cost method of accounting and losses recognized for other than temporary impairments (OTTI) of the subject investments.

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Gain (loss) from sale or disposal of an organization or integrated set of activities (for example, but not limited to, a partnership or corporation) engaged in providing a product or service in a commercial, industrial, or professional environment.

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Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

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This element represents the income or loss from continuing operations attributable to the economic entity which may also be defined as revenue less expenses from ongoing operations, after income or loss from equity method investments, but before income taxes, extraordinary items, and noncontrolling interest.

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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 Net Income (Loss) attributable to noncontrolling interest.

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Interest and Dividend Income (Loss), Securities, Closed Block Variable Annuity

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Other Adjustments to Operating Income (Loss)

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