Deferred Policy Acquisition Costs - Narrative (Details)	Dec. 31, 2017	Dec. 31, 2016
Minimum [Member]
Deferred policy acquisition costs [Line Items]
Long-Duration Contracts, Assumptions by Product and Guarantee, Estimated Investment Yield	3.50%	3.50%
Maximum [Member]
Deferred policy acquisition costs [Line Items]
Long-Duration Contracts, Assumptions by Product and Guarantee, Estimated Investment Yield	7.00%	7.00%