Fair Value Measurements - Changes in balances of Level 3 financial assets carried at fair value (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	$ 1,230	$ 1,102
Total realized/unrealized gains (losses) included in Net income	18	1
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	0	6
Purchases and issuances	92	84
Sales and settlements	(13)	(41)
Transfer into Level 3	0	4
Transfer out of Level 3	(30)	(28)
Financial assets, Ending Balance	1,297	1,128
Fixed maturities:
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	736	664
Total realized/unrealized gains (losses) included in Net income	(1)	5
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	0	6
Purchases and issuances	48	51
Sales and settlements	(11)	(19)
Transfer into Level 3	0	4
Transfer out of Level 3	(30)	(6)
Financial assets, Ending Balance	742	705
U.S. government agency
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	0	0
Total realized/unrealized gains (losses) included in Net income	0	0
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	0	0
Purchases and issuances	0	0
Sales and settlements	0	0
Transfer into Level 3	0	0
Transfer out of Level 3	0	0
Financial assets, Ending Balance	0	0
State and municipal
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	2	5
Total realized/unrealized gains (losses) included in Net income	0	0
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	0	0
Purchases and issuances	0	0
Sales and settlements	0	0
Transfer into Level 3	0	0
Transfer out of Level 3	0	0
Financial assets, Ending Balance	2	5
Residential MBS
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	2	9
Total realized/unrealized gains (losses) included in Net income	0	0
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	0	0
Purchases and issuances	0	0
Sales and settlements	0	(3)
Transfer into Level 3	0	4
Transfer out of Level 3	0	(5)
Financial assets, Ending Balance	2	5
Commercial MBS
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	0	0
Total realized/unrealized gains (losses) included in Net income	0	0
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	0	0
Purchases and issuances	0	0
Sales and settlements	0	0
Transfer into Level 3	0	0
Transfer out of Level 3	0	0
Financial assets, Ending Balance	0	0
Collateralized loan obligations
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	1	2
Total realized/unrealized gains (losses) included in Net income	0	0
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	0	0
Purchases and issuances	0	0
Sales and settlements	0	0
Transfer into Level 3	0	0
Transfer out of Level 3	0	(1)
Financial assets, Ending Balance	1	1
Other asset-backed securities
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	351	329
Total realized/unrealized gains (losses) included in Net income	0	0
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	0	4
Purchases and issuances	15	7
Sales and settlements	(5)	(5)
Transfer into Level 3	0	0
Transfer out of Level 3	(26)	0
Financial assets, Ending Balance	335	335
Corporate and other
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	380	319
Total realized/unrealized gains (losses) included in Net income	(1)	5
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	0	2
Purchases and issuances	33	44
Sales and settlements	(6)	(11)
Transfer into Level 3	0	0
Transfer out of Level 3	(4)	0
Financial assets, Ending Balance	402	359
Equity securities
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	485	427
Total realized/unrealized gains (losses) included in Net income	20	(3)
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	0	0
Purchases and issuances	42	31
Sales and settlements	(2)	(22)
Transfer into Level 3	0	0
Transfer out of Level 3	0	(22)
Financial assets, Ending Balance	545	411
Assets of MIE
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	9	11
Total realized/unrealized gains (losses) included in Net income	(1)	(1)
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	0	0
Purchases and issuances	2	2
Sales and settlements	0	0
Transfer into Level 3	0	0
Transfer out of Level 3	0	0
Financial assets, Ending Balance	$ 10	$ 12