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	Jun. 30, 2026	Dec. 31, 2025
Summary of Investment Holdings [Line Items]
Amortized Cost	$ 59,349	$ 53,961
Allowance for Credit Loss	24	11
Gross Unrealized Gains	331	592
Gross Unrealized Losses	3,914	3,751
Fair Value	55,742	50,791
U.S. government securities
Summary of Investment Holdings [Line Items]
Amortized Cost	4,335	3,854
Allowance for Credit Loss	0	0
Gross Unrealized Gains	0	2
Gross Unrealized Losses	866	851
Fair Value	3,469	3,005
Other government securities
Summary of Investment Holdings [Line Items]
Amortized Cost	1,288	1,254
Allowance for Credit Loss	0	0
Gross Unrealized Gains	8	4
Gross Unrealized Losses	184	193
Fair Value	1,112	1,065
Public utilities
Summary of Investment Holdings [Line Items]
Amortized Cost	7,155	6,529
Allowance for Credit Loss	0	0
Gross Unrealized Gains	47	75
Gross Unrealized Losses	504	458
Fair Value	6,698	6,146
Corporate securities
Summary of Investment Holdings [Line Items]
Amortized Cost	36,891	34,515
Allowance for Credit Loss	5	0
Gross Unrealized Gains	236	443
Gross Unrealized Losses	2,141	2,042
Fair Value	34,981	32,916
Residential mortgage-backed
Summary of Investment Holdings [Line Items]
Amortized Cost	456	445
Allowance for Credit Loss	1	4
Gross Unrealized Gains	20	24
Gross Unrealized Losses	29	23
Fair Value	446	442
Commercial mortgage-backed
Summary of Investment Holdings [Line Items]
Amortized Cost	2,087	1,873
Allowance for Credit Loss	0	0
Gross Unrealized Gains	4	10
Gross Unrealized Losses	62	54
Fair Value	2,029	1,829
Other asset-backed securities
Summary of Investment Holdings [Line Items]
Amortized Cost	7,137	5,491
Allowance for Credit Loss	18	7
Gross Unrealized Gains	16	34
Gross Unrealized Losses	128	130
Fair Value	$ 7,007	$ 5,388