Investments OTTI Credit Losses Recognized in Earnings (Detail) - Fixed maturities - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Beginning balance	$ 11.5	$ 12.5	$ 11.5	$ 12.8
Reductions for securities sold/matured	(11.4)	0.0	(11.2)	0.0
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Changes in Cash Flows	0.2	(0.3)	0.0	(0.6)
Ending balance	0.3	12.2	0.3	12.2
Residential mortgage-backed securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Beginning balance	11.4	12.1	11.1	12.4
Reductions for securities sold/matured	(11.4)	0.0	(10.9)	0.0
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Changes in Cash Flows	0.2	(0.3)	0.0	(0.6)
Ending balance	0.2	11.8	0.2	11.8
Commercial mortgage-backed securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Beginning balance	0.1	0.4	0.4	0.4
Reductions for securities sold/matured	0.0	0.0	(0.3)	0.0
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Changes in Cash Flows	0.0	0.0	0.0	0.0
Ending balance	$ 0.1	$ 0.4	$ 0.1	$ 0.4

Current period changes in the cumulative amount of credit losses recognized in earnings for an other than temporary impairment (OTTI) of a debt security held due to changes in the cash flows expected to be collected and recognized over the remaining lives of the securities.

No definition available.

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- Definition

The cumulative amount of credit losses recognized in earnings related to debt securities held for which a portion of an other than temporary impairment (OTTI) was recognized in other comprehensive income (a component of shareholders' equity).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 8B
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=SL6284393-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 8B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=SL6284393-111563

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- Definition

This item represents reductions in the cumulative amount of credit losses recognized in earnings for an other than temporary impairment (OTTI) of a debt security because of the sale of impaired securities during the period.

+ References

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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