Reinsurance (Reinsurance amounts included in the Statements of Financial Position) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Effects of Reinsurance [Line Items]
Reinsurance recoverables	$ 42,921,981	$ 34,682,127
Policy loans	1,283,214	1,236,077
Deferred policy acquisition costs	1,730,067	1,613,922
Other assets	457,574	365,219
Future policy benefits	27,739,084	19,476,394
Other liabilities	1,429,374	1,093,143
Impacts of Reinsurance
Effects of Reinsurance [Line Items]
Reinsurance recoverables	42,921,981	34,682,127
Policy loans	(138,789)	(130,502)
Deferred policy acquisition costs	(6,862,482)	(7,267,847)
Deferred sales inducements	(528,629)	(562,052)
Other assets	269,342	185,573
Policyholders’ account balances	4,950,024	5,004,112
Future policy benefits	4,173,094	3,376,048
Other liabilities	921,850	621,856
Unaffiliated activity
Effects of Reinsurance [Line Items]
Other assets	0	100
Other liabilities	$ 39,000	$ 27,000