Fair Values of Financial Instruments (Assets and Liabilities Measured on a Recurring Basis by Fair Value Hierarchy) (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Assets
Derivative instruments	$ 1,617,000	$ 1,207,288
Market risk benefits	524,598	479,694
Liabilities
Market risk benefits	3,122,918	3,146,554
Fair Value, Measurements, Recurring
Assets
Real estate investments	1,248,703	1,217,271
Limited partnerships and limited liability companies	501,084	506,685
Derivative instruments	1,617,000	1,207,288
Cash and cash equivalents	13,495,847	9,772,586
Market risk benefits	524,598	479,694
Assets	49,782,753	49,759,517
Liabilities
Market risk benefits	3,122,918	3,146,554
Liabilities	8,098,071	8,071,672
Fair Value, Measurements, Recurring | U.S. Government and agencies
Assets
Investments	27,137	171,141
Fair Value, Measurements, Recurring | States, municipalities and territories
Assets
Investments	2,816,974	3,098,940
Fair Value, Measurements, Recurring | Foreign corporate securities and foreign governments
Assets
Investments	433,008	493,739
Fair Value, Measurements, Recurring | Corporate securities
Assets
Investments	19,264,788	20,603,416
Fair Value, Measurements, Recurring | Residential mortgage backed securities
Assets
Investments	995,130	1,402,501
Fair Value, Measurements, Recurring | Commercial mortgage backed securities
Assets
Investments	2,734,085	2,952,547
Fair Value, Measurements, Recurring | Other asset backed securities
Assets
Investments	5,773,257	6,058,198
Fair Value, Measurements, Recurring | Other investments
Assets
Investments	351,142	1,795,511
Fair Value, Measurements, Recurring | Funds withheld liability - embedded derivative
Liabilities
Derivative liabilities	(298,254)	(256,776)
Fair Value, Measurements, Recurring | Fixed index annuities - embedded derivatives
Liabilities
Derivative liabilities	5,273,407	5,181,894
Fair Value, Measurements, Recurring | NAV
Assets
Real estate investments	0	0
Limited partnerships and limited liability companies	358,429	353,554
Derivative instruments	0	0
Cash and cash equivalents	0	0
Market risk benefits	0	0
Assets	358,429	353,554
Liabilities
Market risk benefits	0	0
Liabilities	0	0
Fair Value, Measurements, Recurring | NAV | U.S. Government and agencies
Assets
Investments	0	0
Fair Value, Measurements, Recurring | NAV | States, municipalities and territories
Assets
Investments	0	0
Fair Value, Measurements, Recurring | NAV | Foreign corporate securities and foreign governments
Assets
Investments	0	0
Fair Value, Measurements, Recurring | NAV | Corporate securities
Assets
Investments	0	0
Fair Value, Measurements, Recurring | NAV | Residential mortgage backed securities
Assets
Investments	0	0
Fair Value, Measurements, Recurring | NAV | Commercial mortgage backed securities
Assets
Investments	0	0
Fair Value, Measurements, Recurring | NAV | Other asset backed securities
Assets
Investments	0	0
Fair Value, Measurements, Recurring | NAV | Other investments
Assets
Investments	0	0
Fair Value, Measurements, Recurring | NAV | Funds withheld liability - embedded derivative
Liabilities
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | NAV | Fixed index annuities - embedded derivatives
Liabilities
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1)
Assets
Real estate investments	0	0
Limited partnerships and limited liability companies	0	0
Derivative instruments	0	0
Cash and cash equivalents	13,495,847	9,772,586
Market risk benefits	0	0
Assets	13,653,373	10,675,775
Liabilities
Market risk benefits	0	0
Liabilities	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1) | U.S. Government and agencies
Assets
Investments	17,068	27,593
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1) | States, municipalities and territories
Assets
Investments	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1) | Foreign corporate securities and foreign governments
Assets
Investments	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1) | Corporate securities
Assets
Investments	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1) | Residential mortgage backed securities
Assets
Investments	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1) | Commercial mortgage backed securities
Assets
Investments	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1) | Other asset backed securities
Assets
Investments	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1) | Other investments
Assets
Investments	140,458	875,596
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1) | Funds withheld liability - embedded derivative
Liabilities
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1) | Fixed index annuities - embedded derivatives
Liabilities
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Assets
Real estate investments	0	0
Limited partnerships and limited liability companies	0	0
Derivative instruments	1,617,000	1,207,288
Cash and cash equivalents	0	0
Market risk benefits	0	0
Assets	30,982,601	34,811,464
Liabilities
Market risk benefits	0	0
Liabilities	0	0
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | U.S. Government and agencies
Assets
Investments	10,069	143,548
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | States, municipalities and territories
Assets
Investments	2,612,223	2,876,723
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Foreign corporate securities and foreign governments
Assets
Investments	433,008	493,739
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Corporate securities
Assets
Investments	19,054,472	20,347,979
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Residential mortgage backed securities
Assets
Investments	972,609	1,402,501
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Commercial mortgage backed securities
Assets
Investments	2,734,085	2,952,547
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Other asset backed securities
Assets
Investments	3,488,452	4,467,224
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Other investments
Assets
Investments	60,683	919,915
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Funds withheld liability - embedded derivative
Liabilities
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Fixed index annuities - embedded derivatives
Liabilities
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Assets
Real estate investments	1,248,703	1,217,271
Limited partnerships and limited liability companies	142,655	153,131
Derivative instruments	0	0
Cash and cash equivalents	0	0
Market risk benefits	524,598	479,694
Assets	4,788,350	3,918,724
Liabilities
Market risk benefits	3,122,918	3,146,554
Liabilities	8,098,071	8,071,672
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | U.S. Government and agencies
Assets
Investments	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | States, municipalities and territories
Assets
Investments	204,751	222,217
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Foreign corporate securities and foreign governments
Assets
Investments	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Corporate securities
Assets
Investments	210,316	255,437
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Residential mortgage backed securities
Assets
Investments	22,521	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Commercial mortgage backed securities
Assets
Investments	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Other asset backed securities
Assets
Investments	2,284,805	1,590,974
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Other investments
Assets
Investments	150,001	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Funds withheld liability - embedded derivative
Liabilities
Derivative liabilities	(298,254)	(256,776)
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Fixed index annuities - embedded derivatives
Liabilities
Derivative liabilities	$ 5,273,407	$ 5,181,894