Closed Block - Change in Maximum Future Earnings (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Change in maximum future earnings of the Closed Block
Maximum future earnings to be recognized from Closed Block assets and liabilities, Beginning of year	$ 549.8	$ 596.4	$ 648.9
Maximum future earnings to be recognized from Closed Block assets and liabilities, End of year	532.1	549.8	596.4
Closed Block revenues, net of Closed Block expenses, income taxes and funding adjustment charges	$ (17.7)	$ (46.6)	$ (52.5)

The carrying amount of closed block liabilities in excess of the carrying amount of closed block assets at the date of demutualization (adjusted to eliminate the impact of related amounts in accumulated other comprehensive income).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 805
-Section 55
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=84167291&loc=d3e31071-158570

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 805
-Section 50
-Paragraph 3
-Subparagraph (b)(9)
-URI http://asc.fasb.org/extlink&oid=6487222&loc=d3e30806-158569

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- Definition

Amount of increase (decrease) of closed block liabilities in excess of closed block assets at the date of demutualization.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 805
-Section 50
-Paragraph 3
-Subparagraph (b)(9)
-URI http://asc.fasb.org/extlink&oid=6487222&loc=d3e30806-158569

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 805
-Section 55
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=84167291&loc=d3e31071-158570

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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.

+ Details

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