Claim, Claim Adjustment Expense and Future Policy Benefit Reserves, Excess Workers' Compensation LPT (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
	Feb. 05, 2021	Mar. 31, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Jan. 01, 2020
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Reinsurance recoverable			$ 5,463	$ 4,457
Claims paid			4,844	$ 5,164	$ 5,576
Outstanding reserves maintained as security for obligations			634
Non-insurance warranty – CNA Financial | Loss Portfolio Transfer for Workers' Compensation Liabilities
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Reinsurance recoverable			$ 690			$ 690
Payment for Reinsurance Premium	$ 697
Claims paid	$ 64
Loss contingency, after tax and noncontrolling interests		$ 11
Non-insurance warranty – CNA Financial | Loss Portfolio Transfer for Workers' Compensation Liabilities | Maximum
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Reinsurance recoverable						$ 1,000