Policyholders' Liabilities (Policyholders' Account Balances) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Liability for Policyholders' Account Balances, by Product Segment [Line Items]
Total policyholders’ account balances	$ 4,846,152	$ 4,736,889
Interest-sensitive life contracts
Liability for Policyholders' Account Balances, by Product Segment [Line Items]
Total policyholders’ account balances	15,301	15,666
Individual annuities
Liability for Policyholders' Account Balances, by Product Segment [Line Items]
Total policyholders’ account balances	4,162,138	1,441,126
Guaranteed interest accounts
Liability for Policyholders' Account Balances, by Product Segment [Line Items]
Total policyholders’ account balances	668,713	893,419
Assumed | Pruco Life
Liability for Policyholders' Account Balances, by Product Segment [Line Items]
Total policyholders’ account balances	$ 0	$ 2,386,678