Reserve for Unpaid Losses and Loss Adjustment Expenses - P&C Prior Accident Years Reserve Development (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Segment Reconciling Items | Asbestos and Environmental
Prior accident year development	$ 0	$ 0
Segment Reconciling Items | Catastrophe
Prior accident year development	0	(3)
Accident and Health Insurance Product Line [Member] | Segment Reconciling Items
Prior accident year development	(61)	(45)
Accident and Health Insurance Product Line [Member] | Segment Reconciling Items | COVID-19 related Claims
Prior accident year development	20
Change in Workers Compensation Discount Including Accretion [Member] | Segment Reconciling Items
Prior accident year development	11	9
General Liability [Member] | Segment Reconciling Items
Prior accident year development	12	12
Marine | Segment Reconciling Items
Prior accident year development	1	0
Package Business [Member] | Segment Reconciling Items
Prior accident year development	(5)	(11)
Property Insurance [Member] | Commercial Lines | Segment Reconciling Items
Prior accident year development	5	(15)
Property Insurance [Member] | Personal Lines | Segment Reconciling Items
Prior accident year development	(1)	0
Professional Liability Insurance [Member] | Segment Reconciling Items
Prior accident year development	0	0
Surety Product Line [Member] | Segment Reconciling Items
Prior accident year development	0	0
Assumed reinsurance | Segment Reconciling Items
Prior accident year development	2	12
Automobiles [Member] | Commercial Lines | Segment Reconciling Items
Prior accident year development	0	0
Automobiles [Member] | Personal Lines | Segment Reconciling Items
Prior accident year development	0	(5)
Uncollectible reinsurance | Segment Reconciling Items
Prior accident year development	8	0
Insurance, Other [Member] | Segment Reconciling Items
Prior accident year development	28	10
Property, Liability and Casualty Insurance Product Line
Prior accident year development	$ 0	$ (36)