Fair Value Measurements - Changes in balances of Level 3 financial assets carried at fair value (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022	Dec. 31, 2021
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	$ 1,102	$ 926
Total realized/unrealized gains (losses) included in Net income	1	23
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	6	(21)
Purchases and issuances	84	105
Sales and settlements	(41)	(27)
Transfer into Level 3	4	37
Transfer out of Level 3	(28)	(45)
Financial assets, Ending Balance	1,128	998
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value	(25)	(23)	$ (25)	$ (23)
Contingent consideration — acquisitions
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value	(25)	(23)	$ (25)	$ (23)
Fixed maturities
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	664	600
Total realized/unrealized gains (losses) included in Net income	5	2
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	6	(21)
Purchases and issuances	51	75
Sales and settlements	(19)	(24)
Transfer into Level 3	4	34
Transfer out of Level 3	(6)	(41)
Financial assets, Ending Balance	705	625
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	5	41
Total realized/unrealized gains (losses) included in Net income	0	0
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	0	(2)
Purchases and issuances	0	0
Sales and settlements	0	(1)
Transfer into Level 3	0	0
Transfer out of Level 3	0	(5)
Financial assets, Ending Balance	5	33
Residential MBS
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	9	14
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	(3)	(1)
Transfer into Level 3	4	0
Transfer out of Level 3	(5)	(2)
Financial assets, Ending Balance	5	11
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	2	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	(1)	0
Financial assets, Ending Balance	1	0
Other asset-backed securities
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	329	278
Total realized/unrealized gains (losses) included in Net income	0	2
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	4	(9)
Purchases and issuances	7	47
Sales and settlements	(5)	(15)
Transfer into Level 3	0	34
Transfer out of Level 3	0	0
Financial assets, Ending Balance	335	337
Corporate and other
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	319	267
Total realized/unrealized gains (losses) included in Net income	5	0
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	2	(10)
Purchases and issuances	44	28
Sales and settlements	(11)	(7)
Transfer into Level 3	0	0
Transfer out of Level 3	0	(34)
Financial assets, Ending Balance	359	244
Equity securities
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	427	313
Total realized/unrealized gains (losses) included in Net income	(3)	22
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	0	0
Purchases and issuances	31	30
Sales and settlements	(22)	(3)
Transfer into Level 3	0	3
Transfer out of Level 3	(22)	(4)
Financial assets, Ending Balance	411	361
Assets of MIE
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	11	13
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	0
Sales and settlements	0	0
Transfer into Level 3	0	0
Transfer out of Level 3	0	0
Financial assets, Ending Balance	$ 12	$ 12