Claim, Claim Adjustment Expense and Future Policy Benefit Reserves, Net Liability for Unpaid Claim and Claim Adjustment Expenses (Details) - USD ($) $ in Millions		Dec. 31, 2020		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net Liability for Unpaid Claim and Claim Adjustment Expenses [Abstract]
Net claim and claim adjustment expenses		$ 18,701		$ 17,885	$ 17,965	$ 18,070
Total reinsurance receivables		4,005	[1]	3,835	4,019	3,934
Total gross liability for unpaid claims and claims adjustment expenses		22,706		21,720	$ 21,984	$ 22,004
Property & Casualty Operations [Member]
Net Liability for Unpaid Claim and Claim Adjustment Expenses [Abstract]
Net claim and claim adjustment expenses		14,924		14,153
Total reinsurance receivables	[1]	1,956
Other Insurance Operations [Member]
Net Liability for Unpaid Claim and Claim Adjustment Expenses [Abstract]
Net claim and claim adjustment expenses		3,777	[2]	$ 3,732
Total reinsurance receivables	[1],[3]	$ 2,049

[1] Reinsurance receivables presented are gross of the allowance for uncollectible reinsurance and do not include reinsurance receivables related to paid losses.

[2] Other Insurance Operations amounts are primarily related to long term care claim reserves, which are long duration insurance contracts, but also include amounts related to unfunded structured settlements arising from short duration insurance contracts.

[3] The Other Insurance Operations reinsurance receivables are primarily related to A&EP claims covered under the loss portfolio transfer (“LPT”).