Nature of Operations and Significant Accounting Policies - Contractholder and Policyholder Liabilities (Details) - Individual Life insurance	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Contractholder and Policyholder Liabilities
Participating business as a percentage of life insurance in force (as a percent)	7.00%	7.00%	8.00%
Participating business as a percentage of life insurance policies in force (as a percent)	26.00%	29.00%	33.00%
Participating business as a percentage of life insurance premiums (as a percent)	24.00%	30.00%	31.00%

Percentage of participating insurance contract to insurance contracts in force.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 50
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6483535&loc=d3e16392-158451

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.14(b)(1))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant