Fair Value of Assets and Liabilities - Schedule of Rollforward of Level 3 Assets and Liabilities Held at Fair Value (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Assets
Balance at beginning of period	$ 675	$ 625	$ 676	$ 618
Total gains (losses) included in: Net income	12	24	16	22
Total gains (losses) included in: OCI	0	(2)	1	0
Transfers Into Level 3	0	0	0	16
Transfers Out of Level 3	0	0	0	0
Transfers (to) from held for sale	0		0
Purchases	39	14	94	92
Sales	(2)	(14)	(59)	(98)
Issues	0	0	0	0
Settlements	(1)	0	(5)	(3)
Balance at end of period	$ 723	$ 647	$ 723	$ 647
Net investment income
Total Level 3 gains (losses) included in net income
Fair Value, Asset (Liability), Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net investment income	Net investment income	Net investment income	Net investment income
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net investment income	Net investment income	Net investment income	Net investment income
Gain (loss) included in earnings	$ 0	$ (1)	$ 1	$ (3)
Net gains (losses) on investments and derivatives
Total Level 3 gains (losses) included in net income
Gain (loss) included in earnings	$ 10	$ 16	$ 10	$ 15
Operating costs and expenses
Total Level 3 gains (losses) included in net income
Fair Value, Asset (Liability), Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Operating costs and expenses	Operating costs and expenses	Operating costs and expenses	Operating costs and expenses
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Operating costs and expenses	Operating costs and expenses	Operating costs and expenses	Operating costs and expenses
Gain (loss) included in earnings	$ 2	$ 9	$ 5	$ 10
Municipal
Assets
Balance at beginning of period	7	12	11	21
Total gains (losses) included in: Net income	(2)	0	(2)	3
Total gains (losses) included in: OCI	0	0	0	(1)
Transfers Into Level 3	0	0	0	0
Transfers Out of Level 3	0	0	0	0
Transfers (to) from held for sale	0		0
Purchases	0	0	0	0
Sales	0	(1)	(2)	(10)
Issues	0	0	0	0
Settlements	0	0	(2)	(2)
Balance at end of period	5	11	5	11
Corporate - public
Assets
Balance at beginning of period	30	26	26	69
Total gains (losses) included in: Net income	0	0	1	(1)
Total gains (losses) included in: OCI	0	(1)	1	1
Transfers Into Level 3	0	0	0	0
Transfers Out of Level 3	0	0	0	0
Transfers (to) from held for sale	(7)		7
Purchases	5	0	16	0
Sales	0	0	(9)	(44)
Issues	0	0	0	0
Settlements	0	0	0	0
Balance at end of period	28	25	28	25
Corporate - privately placed
Assets
Balance at beginning of period	50	60	58	55
Total gains (losses) included in: Net income	0	0	(6)	(11)
Total gains (losses) included in: OCI	0	(1)	0	0
Transfers Into Level 3	0	0	0	16
Transfers Out of Level 3	0	0	0	0
Transfers (to) from held for sale	0		0
Purchases	1	0	1	1
Sales	0	0	(2)	(2)
Issues	0	0	0	0
Settlements	0	0	0	0
Balance at end of period	51	59	51	59
ABS
Assets
Balance at beginning of period	71	34	58	28
Total gains (losses) included in: Net income	0	0	0	0
Total gains (losses) included in: OCI	0	0	0	0
Transfers Into Level 3	0	0	0	0
Transfers Out of Level 3	0	0	0	0
Transfers (to) from held for sale	0		0
Purchases	27	4	41	11
Sales	0	0	0	0
Issues	0	0	0	0
Settlements	(1)	0	(2)	(1)
Balance at end of period	97	38	97	38
Fixed income securities
Assets
Balance at beginning of period	158	132	153	173
Total gains (losses) included in: Net income	(2)	0	(7)	(9)
Total gains (losses) included in: OCI	0	(2)	1	0
Transfers Into Level 3	0	0	0	16
Transfers Out of Level 3	0	0	0	0
Transfers (to) from held for sale	(7)		7
Purchases	33	4	58	12
Sales	0	(1)	(13)	(56)
Issues	0	0	0	0
Settlements	(1)	0	(4)	(3)
Balance at end of period	181	133	181	133
Equity securities
Assets
Balance at beginning of period	393	381	402	333
Total gains (losses) included in: Net income	12	15	18	22
Total gains (losses) included in: OCI	0	0	0	0
Transfers Into Level 3	0	0	0	0
Transfers Out of Level 3	0	0	0	0
Transfers (to) from held for sale	0		0
Purchases	5	0	14	70
Sales	(2)	(13)	(26)	(42)
Issues	0	0	0	0
Settlements	0	0	0	0
Balance at end of period	408	383	408	383
Short-term investments
Assets
Balance at beginning of period	1	6	1	6
Total gains (losses) included in: Net income	0	0	0	0
Total gains (losses) included in: OCI	0	0	0	0
Transfers Into Level 3	0	0	0	0
Transfers Out of Level 3	0	0	0	0
Transfers (to) from held for sale	0		0
Purchases	1	10	22	10
Sales	0	0	(20)	0
Issues	0	0	0	0
Settlements	0	0	(1)	0
Balance at end of period	2	16	2	16
Other investments
Assets
Balance at beginning of period	2	2	2	3
Total gains (losses) included in: Net income	0	0	0	(1)
Total gains (losses) included in: OCI	0	0	0	0
Transfers Into Level 3	0	0	0	0
Transfers Out of Level 3	0	0	0	0
Transfers (to) from held for sale	0		0
Purchases	0	0	0	0
Sales	0	0	0	0
Issues	0	0	0	0
Settlements	0	0	0	0
Balance at end of period	2	2	2	2
Other assets
Assets
Balance at beginning of period	121	104	118	103
Total gains (losses) included in: Net income	2	9	5	10
Total gains (losses) included in: OCI	0	0	0	0
Transfers Into Level 3	0	0	0	0
Transfers Out of Level 3	0	0	0	0
Transfers (to) from held for sale	0		0
Purchases	0	0	0	0
Sales	0	0	0	0
Issues	0	0	0	0
Settlements	0	0	0	0
Balance at end of period	123	$ 113	123	$ 113
Assets held for sale
Assets
Balance at beginning of period	0		0
Total gains (losses) included in: Net income	0		0
Total gains (losses) included in: OCI	0		0
Transfers Into Level 3	0		0
Transfers Out of Level 3	0		0
Transfers (to) from held for sale	7		(7)
Purchases	0		0
Sales	0		0
Issues	0		0
Settlements	0		0
Balance at end of period	$ 7		$ 7