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	Sep. 30, 2026	Dec. 31, 2025
Summary of Investment Holdings [Line Items]
Amortized Cost	$ 63,389	$ 53,961
Allowance for Credit Loss	4	11
Gross Unrealized Gains	81	592
Gross Unrealized Losses	5,856	3,751
Fair Value	57,610	50,791
U.S. government securities
Summary of Investment Holdings [Line Items]
Amortized Cost	5,506	3,854
Allowance for Credit Loss	0	0
Gross Unrealized Gains	0	2
Gross Unrealized Losses	1,012	851
Fair Value	4,494	3,005
Other government securities
Summary of Investment Holdings [Line Items]
Amortized Cost	1,307	1,254
Allowance for Credit Loss	0	0
Gross Unrealized Gains	1	4
Gross Unrealized Losses	255	193
Fair Value	1,053	1,065
Public utilities
Summary of Investment Holdings [Line Items]
Amortized Cost	7,537	6,529
Allowance for Credit Loss	0	0
Gross Unrealized Gains	13	75
Gross Unrealized Losses	850	458
Fair Value	6,700	6,146
Corporate securities
Summary of Investment Holdings [Line Items]
Amortized Cost	38,257	34,515
Allowance for Credit Loss	0	0
Gross Unrealized Gains	43	443
Gross Unrealized Losses	3,370	2,042
Fair Value	34,930	32,916
Residential mortgage-backed
Summary of Investment Holdings [Line Items]
Amortized Cost	485	445
Allowance for Credit Loss	1	4
Gross Unrealized Gains	18	24
Gross Unrealized Losses	47	23
Fair Value	455	442
Commercial mortgage-backed
Summary of Investment Holdings [Line Items]
Amortized Cost	2,074	1,873
Allowance for Credit Loss	1	0
Gross Unrealized Gains	1	10
Gross Unrealized Losses	88	54
Fair Value	1,986	1,829
Other asset-backed securities
Summary of Investment Holdings [Line Items]
Amortized Cost	8,223	5,491
Allowance for Credit Loss	2	7
Gross Unrealized Gains	5	34
Gross Unrealized Losses	234	130
Fair Value	$ 7,992	$ 5,388