Investments (Fair Value and Losses by Investment Category and Length of Time in a Loss Position) (Details) - Fixed maturities - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Less than Twelve Months, Fair Value	$ 13,270,425	$ 5,052,071
Less than Twelve Months, Gross Unrealized Losses	2,113,288	94,096
Twelve Months or More, Fair Value	2,368,889	333,294
Twelve Months or More, Gross Unrealized Losses	694,712	19,435
Total, Fair Value	15,639,314	5,385,365
Total, Gross Unrealized Losses	2,808,000	113,531
US Treasury securities and obligations of U.S. government authorities and agencies
Debt Securities, Available-for-sale [Line Items]
Less than Twelve Months, Fair Value	217,869	0
Less than Twelve Months, Gross Unrealized Losses	68,996	0
Twelve Months or More, Fair Value	1,810	2,119
Twelve Months or More, Gross Unrealized Losses	386	111
Total, Fair Value	219,679	2,119
Total, Gross Unrealized Losses	69,382	111
Obligations of U.S. states and their political subdivisions
Debt Securities, Available-for-sale [Line Items]
Less than Twelve Months, Fair Value	426,560	104,621
Less than Twelve Months, Gross Unrealized Losses	48,592	701
Twelve Months or More, Fair Value	5,761	0
Twelve Months or More, Gross Unrealized Losses	1,001	0
Total, Fair Value	432,321	104,621
Total, Gross Unrealized Losses	49,593	701
Foreign government bonds
Debt Securities, Available-for-sale [Line Items]
Less than Twelve Months, Fair Value	218,160	59,550
Less than Twelve Months, Gross Unrealized Losses	53,333	2,826
Twelve Months or More, Fair Value	34,375	6,473
Twelve Months or More, Gross Unrealized Losses	19,174	371
Total, Fair Value	252,535	66,023
Total, Gross Unrealized Losses	72,507	3,197
U.S. public corporate securities
Debt Securities, Available-for-sale [Line Items]
Less than Twelve Months, Fair Value	4,861,137	1,681,201
Less than Twelve Months, Gross Unrealized Losses	901,221	23,160
Twelve Months or More, Fair Value	765,437	180,249
Twelve Months or More, Gross Unrealized Losses	226,568	6,610
Total, Fair Value	5,626,574	1,861,450
Total, Gross Unrealized Losses	1,127,789	29,770
U.S. private corporate securities
Debt Securities, Available-for-sale [Line Items]
Less than Twelve Months, Fair Value	2,663,536	972,796
Less than Twelve Months, Gross Unrealized Losses	296,993	14,036
Twelve Months or More, Fair Value	372,891	16,409
Twelve Months or More, Gross Unrealized Losses	82,415	2,844
Total, Fair Value	3,036,427	989,205
Total, Gross Unrealized Losses	379,408	16,880
Foreign public corporate securities
Debt Securities, Available-for-sale [Line Items]
Less than Twelve Months, Fair Value	921,969	532,445
Less than Twelve Months, Gross Unrealized Losses	128,690	8,255
Twelve Months or More, Fair Value	311,219	29,718
Twelve Months or More, Gross Unrealized Losses	66,112	2,108
Total, Fair Value	1,233,188	562,163
Total, Gross Unrealized Losses	194,802	10,363
Foreign private corporate securities
Debt Securities, Available-for-sale [Line Items]
Less than Twelve Months, Fair Value	2,175,148	1,253,739
Less than Twelve Months, Gross Unrealized Losses	521,284	42,392
Twelve Months or More, Fair Value	669,419	57,637
Twelve Months or More, Gross Unrealized Losses	266,022	5,616
Total, Fair Value	2,844,567	1,311,376
Total, Gross Unrealized Losses	787,306	48,008
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Less than Twelve Months, Fair Value	1,076,306	288,971
Less than Twelve Months, Gross Unrealized Losses	30,456	1,099
Twelve Months or More, Fair Value	131,536	0
Twelve Months or More, Gross Unrealized Losses	13,705	0
Total, Fair Value	1,207,842	288,971
Total, Gross Unrealized Losses	44,161	1,099
Commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Less than Twelve Months, Fair Value	577,269	157,355
Less than Twelve Months, Gross Unrealized Losses	53,865	1,622
Twelve Months or More, Fair Value	76,070	40,689
Twelve Months or More, Gross Unrealized Losses	19,266	1,775
Total, Fair Value	653,339	198,044
Total, Gross Unrealized Losses	73,131	3,397
Residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Less than Twelve Months, Fair Value	132,471	1,393
Less than Twelve Months, Gross Unrealized Losses	9,858	5
Twelve Months or More, Fair Value	371	0
Twelve Months or More, Gross Unrealized Losses	63	0
Total, Fair Value	132,842	1,393
Total, Gross Unrealized Losses	$ 9,921	$ 5