Reinsurance - Consolidated Property Casualty Insurance Assumed and Ceded Business (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Property Casualty Insurance Assumed And Ceded Business
Earned premiums	$ 1,943	$ 1,773	$ 3,861	$ 3,466
Incurred loss and loss expenses	1,340	1,322	2,738	2,354
Consolidated Property And Casualty Insurance
Property Casualty Insurance Assumed And Ceded Business
Direct written premiums	2,071	1,871	3,930	3,574
Assumed written premiums	194	193	438	456
Ceded written premiums	(115)	(100)	(199)	(167)
Net written premiums	2,150	1,964	4,169	3,863
Direct earned premiums	1,806	1,631	3,566	3,192
Assumed earned premiums	134	134	293	255
Ceded earned premiums	(77)	(68)	(155)	(132)
Earned premiums	1,863	1,697	3,704	3,315
Direct incurred loss and loss expenses	1,265	1,174	2,564	2,069
Assumed incurred loss and loss expenses	58	67	134	140
Ceded incurred loss and loss expenses	(61)	(1)	(119)	(13)
Incurred loss and loss expenses	$ 1,262	$ 1,240	$ 2,579	$ 2,196