Reinsurance (Reinsurance amounts included in the Statements of Financial Position) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Effects of Reinsurance [Line Items]
Reinsurance recoverables	$ 36,106,323	$ 34,682,127
Policy loans	1,251,094	1,236,077
Deferred policy acquisition costs	1,675,860	1,613,922
Other assets	378,154	365,219
Future policy benefits	20,943,806	19,476,394
Other liabilities	1,133,756	1,093,143
Impacts of Reinsurance
Effects of Reinsurance [Line Items]
Reinsurance recoverables	36,106,323	34,682,127
Policy loans	(132,433)	(130,502)
Deferred policy acquisition costs	(7,255,866)	(7,267,847)
Deferred sales inducements	(567,015)	(562,052)
Other assets	171,968	185,573
Policyholders’ account balances	4,986,354	5,004,112
Future policy benefits	3,619,334	3,376,048
Other liabilities	653,666	621,856
Unaffiliated activity
Effects of Reinsurance [Line Items]
Other assets	100	100
Other liabilities	$ 39,000	$ 27,000