Summary of Significant Accounting Policies (Recent accounting change) (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net after tax unamortized periodic pension cost	$ (6,667,730)	$ (6,325,797)
Fixed maturity securities, allowance for credit loss	22,625	2,580
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net after tax unamortized periodic pension cost	(9,015,135)	(8,348,381)	$ (7,932,372)	$ (7,558,619)
Accumulated Other Comprehensive Income (Loss)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net after tax unamortized periodic pension cost	$ (90,900)	(289,714)	(124,514)	91,491
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	30,514	0
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	$ (24,952)	$ 0