Liabilities for Unpaid Claims and Claims Expenses - Discounted Liabilities (Details) - USD ($) $ in Billions	Dec. 31, 2016	Dec. 31, 2015
Short-duration Insurance Contracts Discounted Liabilities [Line Items]
Discounted liabilities	$ 3.9	$ 3.7
Aggregate amount of discount	$ 1.1	$ 1.0
Minimum [Member]
Short-duration Insurance Contracts Discounted Liabilities [Line Items]
Discount rate assumptions	3.30%	3.50%
Maximum [Member]
Short-duration Insurance Contracts Discounted Liabilities [Line Items]
Discount rate assumptions	5.80%	5.70%