Investments - Gross Unrealized Appreciation (Depreciation) on Debt Securities by Type of Issuer Including HFS (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Amortized cost, including held for sale assets	$ 10,097	$ 10,379
Allowance for Credit Loss, including held for sale assets	(90)	(33)
Unrealized Appreciation, including held for sale assets	124	195
Unrealized Depreciation, including held for sale assets	(781)	(686)
Fair Value, including held for sale assets	9,350	9,855
Federal government and agency
Debt Securities, Available-for-sale [Line Items]
Amortized cost, including held for sale assets	288	251
Allowance for Credit Loss, including held for sale assets	0	0
Unrealized Appreciation, including held for sale assets	18	24
Unrealized Depreciation, including held for sale assets	(10)	(8)
Fair Value, including held for sale assets	296	267
State and local government
Debt Securities, Available-for-sale [Line Items]
Amortized cost, including held for sale assets	37	37
Allowance for Credit Loss, including held for sale assets	0	0
Unrealized Appreciation, including held for sale assets	1	2
Unrealized Depreciation, including held for sale assets	(1)	(1)
Fair Value, including held for sale assets	37	38
Foreign government
Debt Securities, Available-for-sale [Line Items]
Amortized cost, including held for sale assets	353	355
Allowance for Credit Loss, including held for sale assets	0	0
Unrealized Appreciation, including held for sale assets	6	10
Unrealized Depreciation, including held for sale assets	(14)	(13)
Fair Value, including held for sale assets	345	352
Corporate
Debt Securities, Available-for-sale [Line Items]
Amortized cost, including held for sale assets	9,032	9,338
Allowance for Credit Loss, including held for sale assets	(90)	(33)
Unrealized Appreciation, including held for sale assets	99	158
Unrealized Depreciation, including held for sale assets	(721)	(630)
Fair Value, including held for sale assets	8,320	8,833
Mortgage and other asset-backed
Debt Securities, Available-for-sale [Line Items]
Amortized cost, including held for sale assets	387	398
Allowance for Credit Loss, including held for sale assets	0	0
Unrealized Appreciation, including held for sale assets	0	1
Unrealized Depreciation, including held for sale assets	(35)	(34)
Fair Value, including held for sale assets	$ 352	$ 365