Sales of Businesses - Revenues, costs and expenses, and earnings before income taxes of business disposed (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net earned premiums	$ 1,173	$ 1,209
Losses and loss adjustment expenses	667	707
Commissions and other underwriting expenses	380	420
Net investment income	188	104
Net earnings (loss), including noncontrolling interests	$ 419	(304)
Neon Capital Limited
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net earned premiums		71
Losses and loss adjustment expenses		40
Commissions and other underwriting expenses		32
Underwriting loss		(1)
Net investment income		(6)
Other income and expenses, net		(3)
Net earnings (loss), including noncontrolling interests		$ (10)