Investments - Schedule of Debt Securities - Amortized Cost, Gross Unrealized Gains and Losses, Fair Value and Allowance for Credit Loss and Maturities (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
Summary of Investment Holdings [Line Items]
Amortized Cost	$ 55,707	$ 53,961
Allowance for Credit Loss	17	11
Gross Unrealized Gains	337	592
Gross Unrealized Losses	4,079	3,751
Fair Value	51,948	50,791
U.S. government securities
Summary of Investment Holdings [Line Items]
Amortized Cost	3,989	3,854
Allowance for Credit Loss	0	0
Gross Unrealized Gains	1	2
Gross Unrealized Losses	865	851
Fair Value	3,125	3,005
Other government securities
Summary of Investment Holdings [Line Items]
Amortized Cost	1,255	1,254
Allowance for Credit Loss	0	0
Gross Unrealized Gains	2	4
Gross Unrealized Losses	202	193
Fair Value	1,055	1,065
Public utilities
Summary of Investment Holdings [Line Items]
Amortized Cost	6,696	6,529
Allowance for Credit Loss	0	0
Gross Unrealized Gains	46	75
Gross Unrealized Losses	530	458
Fair Value	6,212	6,146
Corporate securities
Summary of Investment Holdings [Line Items]
Amortized Cost	35,124	34,515
Allowance for Credit Loss	6	0
Gross Unrealized Gains	245	443
Gross Unrealized Losses	2,255	2,042
Fair Value	33,108	32,916
Residential mortgage-backed
Summary of Investment Holdings [Line Items]
Amortized Cost	473	445
Allowance for Credit Loss	1	4
Gross Unrealized Gains	21	24
Gross Unrealized Losses	26	23
Fair Value	467	442
Commercial mortgage-backed
Summary of Investment Holdings [Line Items]
Amortized Cost	2,010	1,873
Allowance for Credit Loss	0	0
Gross Unrealized Gains	5	10
Gross Unrealized Losses	61	54
Fair Value	1,954	1,829
Other asset-backed securities
Summary of Investment Holdings [Line Items]
Amortized Cost	6,160	5,491
Allowance for Credit Loss	10	7
Gross Unrealized Gains	17	34
Gross Unrealized Losses	140	130
Fair Value	$ 6,027	$ 5,388