Summary of Significant Accounting Policies (Recent accounting change) (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net after tax unamortized periodic pension cost	$ (6,768,161)	$ (6,667,730)
Fixed maturity securities, allowance for credit loss	37,466	22,625
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net after tax unamortized periodic pension cost	(10,161,005)	(9,015,135)	$ (8,348,381)	$ (7,932,372)
Accumulated Other Comprehensive Income (Loss)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net after tax unamortized periodic pension cost	$ 892,905	(90,900)	(289,714)	(124,514)
Cumulative Effect, Period Of Adoption, Adjustment | Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net after tax unamortized periodic pension cost		0	0	30,514
Cumulative Effect, Period Of Adoption, Adjustment | Accumulated Other Comprehensive Income (Loss)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net after tax unamortized periodic pension cost		$ 0	$ 0	$ (24,952)