Claim and Claim Adjustment Expense Reserves and Future Policy Benefit Reserves - Life & Group Policyholder Reserves (Details) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2022	Sep. 30, 2021
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Pretax margin included in long term care future policy benefit reserves	$ 125	$ 72
CNA Financial | Release of IBNR Reserves and Higher Claim Severity
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Pretax reductions in claim tax and claim adjustment expense reserves	(25)
CNA Financial | Release of IBNR Reserves
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Pretax reductions in claim tax and claim adjustment expense reserves	(107)
CNA Financial | Higher Claim Severity
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Pretax reductions in claim tax and claim adjustment expense reserves	82
CNA Financial | Lower Discount Rate Assumptions and Mortality Assumption Changes
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Pretax reductions in claim tax and claim adjustment expense reserves	$ (5)	2
CNA Financial | Lower Claim Severity
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Pretax reductions in claim tax and claim adjustment expense reserves		$ (40)