Claim and Claim Adjustment Expense Reserves (Net prior year development) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Segment Reporting Information [Line Items]
Pretax (favorable) unfavorable premium development, excluding Life & Group	$ (12)	$ (15)
Specialty
Segment Reporting Information [Line Items]
Pretax (favorable) unfavorable premium development, excluding Life & Group	(10)	(15)
Commercial
Segment Reporting Information [Line Items]
Pretax (favorable) unfavorable premium development, excluding Life & Group	(2)	0
International
Segment Reporting Information [Line Items]
Pretax (favorable) unfavorable premium development, excluding Life & Group	0	0
Corporate & Other
Segment Reporting Information [Line Items]
Pretax (favorable) unfavorable premium development, excluding Life & Group	$ 0	$ 0