Claim, Claim Adjustment Expense and Future Policy Benefit Reserves, Gross and Net Carried Reserves (Details) - USD ($) $ in Millions	Dec. 31, 2020		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Gross and Net Carried Reserves [Abstract]
Gross case reserves	$ 10,694		$ 10,989
Gross IBNR reserves	12,012		10,731
Total gross carried claim and claim adjustment expense reserves	22,706		21,720
Net case reserves	8,930		9,178
Net IBNR reserves	9,771		8,707
Total net carried claim and claim adjustment expense reserves	18,701		17,885	$ 17,965	$ 18,070
Property and Casualty Operations [Member]
Gross and Net Carried Reserves [Abstract]
Gross case reserves	6,183		6,276
Gross IBNR reserves	10,697		9,494
Total gross carried claim and claim adjustment expense reserves	16,880		15,770
Net case reserves	5,544		5,645
Net IBNR reserves	9,380		8,508
Total net carried claim and claim adjustment expense reserves	14,924		14,153
Other Insurance Operations [Member]
Gross and Net Carried Reserves [Abstract]
Gross case reserves	4,511		4,713
Gross IBNR reserves	1,315		1,237
Total gross carried claim and claim adjustment expense reserves	5,826		5,950
Net case reserves	3,386		3,533
Net IBNR reserves	391		199
Total net carried claim and claim adjustment expense reserves	$ 3,777	[1]	$ 3,732

[1] 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.