Investments (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Schedule of Investments [Line Items]
Loans acquired	$ 0	$ 27,600
Loans sold	0	24,800
Fixed Maturity Purchased with Credit Deterioration	0	0
Securities sold under agreements to repurchase	$ 0	$ 0
Commercial mortgage loans, Percentage	100.00%	100.00%
Commercial mortgage and other loans purchased with credit deterioration	$ 0	$ 0
Fixed maturities, available-for-sale	26,131,780	19,025,401
Fixed maturities, trading	2,796,446	1,936,159
Fair value of collateral that could be sold or repledged	25,000	290,000
Assets Deposited With Governmental Authorities	3,600	3,900
Gross Unrealized Losses	1,739,561	2,353,479
Twelve Months or More, Gross Unrealized Losses	1,699,993	1,428,069
Carrying value of non-income producing assets
Schedule of Investments [Line Items]
Fixed maturities, available-for-sale	9,200
Fixed maturities, trading	1,000
Fixed maturities | Trading
Schedule of Investments [Line Items]
Fixed maturities, trading	2,796,446
NAIC high or highest quality rating | Fixed maturities
Schedule of Investments [Line Items]
Gross Unrealized Losses	1,633,900	2,164,100
NAIC other than high or highest quality rating | Fixed maturities
Schedule of Investments [Line Items]
Gross Unrealized Losses	$ 105,700	189,400
California
Schedule of Investments [Line Items]
Commercial mortgage loans, Percentage	28.00%
Texas
Schedule of Investments [Line Items]
Commercial mortgage loans, Percentage	12.00%
Colorado
Schedule of Investments [Line Items]
Commercial mortgage loans, Percentage	5.00%
Europe
Schedule of Investments [Line Items]
Commercial mortgage loans, Percentage	10.00%
Mexico
Schedule of Investments [Line Items]
Commercial mortgage loans, Percentage	1.00%
Australia
Schedule of Investments [Line Items]
Commercial mortgage loans, Percentage	1.00%
Other Income | Fixed maturities | Trading
Schedule of Investments [Line Items]
Unrealized Gain (Loss) on Investments	$ 65,600	(728,600)	$ 156,100
Other Income | Equity securities
Schedule of Investments [Line Items]
Unrealized Gain (Loss) on Investments	25,800	(10,200)	$ 2,100
Fixed maturities
Schedule of Investments [Line Items]
Twelve Months or More, Gross Unrealized Losses	$ 1,700,000	$ 1,428,100