Summary of Significant Accounting Policies Participating Policies (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Weighted Average Discount Rates [Line Items]
Participating Policies Additional Income Allocated, Percent	62.50%	62.20%
Minimum [Member]
Weighted Average Discount Rates [Line Items]
Weighted Average Discount Rate, Percent	3.20%
Number of Years, Future Scaling Rate	1
Minimum [Member] | One Year [Domain] [Domain]
Weighted Average Discount Rates [Line Items]
Weighted Average Discount Rate Percent, Future Scaling Rate	3.19%
Maximum [Member]
Weighted Average Discount Rates [Line Items]
Weighted Average Discount Rate, Percent	9.00%
Number of Years, Future Scaling Rate	20
Maximum [Member] | Fifteen Years and After [Member]
Weighted Average Discount Rates [Line Items]
Weighted Average Discount Rate Percent, Future Scaling Rate	4.45%