Reinsurance - Consolidated Property Casualty Insurance Assumed and Ceded Business (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Property Casualty Insurance Assumed And Ceded Business
Earned premiums	$ 1,690	$ 1,544
Incurred loss and loss expenses	1,039	1,003
Consolidated Property And Casualty Insurance
Property Casualty Insurance Assumed And Ceded Business
Direct written premiums	1,703	1,545
Assumed written premiums	263	205
Ceded written premiums	(67)	(57)
Net written premiums	1,899	1,693
Direct earned premiums	1,561	1,429
Assumed earned premiums	121	101
Ceded earned premiums	(64)	(55)
Earned premiums	1,618	1,475
Direct incurred loss and loss expenses	895	868
Assumed incurred loss and loss expenses	73	78
Ceded incurred loss and loss expenses	(12)	(23)
Incurred loss and loss expenses	$ 956	$ 923