Claim and Claim Adjustment Expense Reserves and Future Policy Benefit Reserves - Life and Group Policyholder Reserves (Details) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2022	Sep. 30, 2021
Long Term Care Policyholder Reserves [Abstract]
Pretax margin included in long term care future policy benefit reserves	$ 125	$ 72
CNA | Release of IBNR Reserves And Higher Claim Severity
Long Term Care Policyholder Reserves [Abstract]
Pretax change in claim tax and claim adjustment expense reserves	(25)
CNA | Release of IBNR Reserves
Long Term Care Policyholder Reserves [Abstract]
Pretax change in claim tax and claim adjustment expense reserves	(107)
CNA | Higher Claim Severity
Long Term Care Policyholder Reserves [Abstract]
Pretax change in claim tax and claim adjustment expense reserves	82
CNA | Lower Discount Rate Assumptions and Mortality Assumption Changes
Long Term Care Policyholder Reserves [Abstract]
Pretax change in claim tax and claim adjustment expense reserves	$ (5)	2
CNA | Lower Claim Severity
Long Term Care Policyholder Reserves [Abstract]
Pretax change in claim tax and claim adjustment expense reserves		$ (40)