Sales of Businesses - Revenues, costs and expenses, and earnings before income taxes of business disposed (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net earned premiums	$ 1,529	$ 1,381	$ 3,952	$ 3,774
Losses and loss adjustment expenses	954	963	2,335	2,441
Commissions and other underwriting expenses	417	406	1,187	1,235
Net investment income	169	122	521	314
Net earnings, including noncontrolling interests	$ 219	164	$ 1,640	27
Neon Capital Limited
Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net earned premiums		42		174
Losses and loss adjustment expenses		60		166
Commissions and other underwriting expenses		20		90
Underwriting loss		(38)		(82)
Net investment income		1		(5)
Other income and expenses, net		(3)		(5)
Net earnings, including noncontrolling interests		$ (40)		$ (92)