Significant Accounting Policies and Pronouncements (Impact of Change in Accounting for Certain Reinsurance Contracts) (Details) - USD ($) $ in Thousands	3 Months Ended									12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Change in Accounting Estimate [Line Items]
Decrease in Policy charges and fee income										$ 544,156	$ 533,327	$ 275,693
Decrease in Policyholders' benefits										153,074	149,499	(18,416)
Increase in Amortization of deferred policy acquisition costs										113,318	135,826	95,007
Pre-tax charge to income	$ 34,411	$ 38,637	$ 14,122	$ 71,614	$ 8,667	$ 16,570	$ 23,307	$ 9,243		158,784	57,787	171,450
Other liabilities	1,390,876				1,093,143					1,390,876	1,093,143
Reinsurance recoverables	40,710,159				34,682,127					40,710,159	34,682,127
Policyholders’ account balances	22,878,823				22,059,692					22,878,823	22,059,692
Deferred policy acquisition costs	$ 1,855,698				$ 1,613,922					$ 1,855,698	$ 1,613,922	$ 1,376,211	$ 1,341,093
Individual Life | Accounting for Certain Reinsurance Contracts
Change in Accounting Estimate [Line Items]
Decrease in Policy charges and fee income									$ (236,000)
Decrease in Policyholders' benefits									253,000
Increase in Amortization of deferred policy acquisition costs									(19,000)
Pre-tax charge to income									(2,000)
Other liabilities									284,000
Reinsurance recoverables									247,000
Policyholders’ account balances									(48,000)
Deferred policy acquisition costs									(19,000)
Future policy benefits									$ (6,000)