Reinsurance - Consolidated Property Casualty Insurance Assumed and Ceded Business (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Property Casualty Insurance Assumed And Ceded Business
Earned premiums	$ 1,882	$ 1,669	$ 5,345	$ 4,806
Incurred loss and loss expenses	1,418	1,072	3,766	2,990
Consolidated Property And Casualty Insurance
Property Casualty Insurance Assumed And Ceded Business
Direct written premiums	1,730	1,527	5,304	4,721
Assumed written premiums	92	66	548	432
Ceded written premiums	(72)	(55)	(239)	(208)
Net written premiums	1,750	1,538	5,613	4,945
Direct earned premiums	1,743	1,553	4,935	4,447
Assumed earned premiums	161	117	416	327
Ceded earned premiums	(95)	(74)	(227)	(189)
Earned premiums	1,809	1,596	5,124	4,585
Direct incurred loss and loss expenses	1,247	876	3,316	2,525
Assumed incurred loss and loss expenses	164	165	304	297
Ceded incurred loss and loss expenses	(63)	(53)	(76)	(81)
Incurred loss and loss expenses	$ 1,348	$ 988	$ 3,544	$ 2,741