Policyholders' Liabilities (Future Policy Benefits) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Liability for Future Policy Benefit, by Product Segment [Line Items]
Life insurance – domestic	$ 800	$ 964
Individual and group annuities and supplementary contracts	970,936	446,318
Other contract liabilities	8,160,833	1,267,739
Total future policy benefits	9,132,569	8,686,196
Assumed | Pruco Life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Other contract liabilities	0	6,442,965
Individual and group annuities assumed upon reinsurance agreement with Pruco Life	$ 0	$ 528,210