Reconciliation of Total Revenue and Income (Loss) before Income Tax by Segment to Adjusted Operating Revenue and Adjusted Operating Income (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting, Revenue Reconciling Item
Total Revenue	$ 2,927.8	$ 2,819.1	$ 8,717.7	$ 8,447.6
Net Realized Investment Gain	6.7	9.8	1.9	28.9
Income (Loss) Before Income Tax Expense (Benefit)	(377.8)	366.8	318.1	1,058.7
Net Realized Investment Gain	6.7	9.8	1.9	28.9
Long-term Care Reserve Increase	(750.8)		(750.8)
Operating Segments
Segment Reporting, Revenue Reconciling Item
Total Revenue	2,927.8	2,819.1	8,717.7	8,447.6
Net Realized Investment Gain	6.7	9.8	1.9	28.9
Adjusted Operating Revenue	2,921.1	2,809.3	8,715.8	8,418.7
Income (Loss) Before Income Tax Expense (Benefit)	(377.8)	366.8	318.1	1,058.7
Net Realized Investment Gain	6.7	9.8	1.9	28.9
Loss Related to Guaranty Fund Assessment	0.0	0.0	0.0	(20.6)
Long-term Care Reserve Increase	(750.8)	0.0	(750.8)	0.0
Adjusted Operating Income (Loss)	$ 366.3	$ 357.0	$ 1,067.0	$ 1,050.4

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Long-term Care Reserve Increase, Before Tax

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The net result for the period of deducting operating expenses from operating revenues.

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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