Reinsurance - Consolidated Property Casualty Insurance Assumed and Ceded Business (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Property Casualty Insurance Assumed And Ceded Business
Earned premiums	$ 1,918	$ 1,693
Incurred loss and loss expenses	1,398	1,032
Consolidated Property And Casualty Insurance
Property Casualty Insurance Assumed And Ceded Business
Direct written premiums	1,859	1,703
Assumed written premiums	244	263
Ceded written premiums	(84)	(67)
Net written premiums	2,019	1,899
Direct earned premiums	1,760	1,561
Assumed earned premiums	159	121
Ceded earned premiums	(78)	(64)
Earned premiums	1,841	1,618
Direct incurred loss and loss expenses	1,299	895
Assumed incurred loss and loss expenses	76	73
Ceded incurred loss and loss expenses	(58)	(12)
Incurred loss and loss expenses	$ 1,317	$ 956