Schedule VI (SUPPLEMENTARY INFORMATION CONCERNING PROPERTY AND CASUALTY OPERATIONS) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters [Abstract]
Deferred Policy Acquisition Costs		$ 4,161	$ 3,926	$ 3,805
Net Reserves for Unpaid Losses		48,509	48,271	49,165
Unearned Premiums		16,771	15,532	15,216
Net Premiums Earned		30,189	29,042	28,054
Net Investment Income		3,141	3,047	2,890
Current Year Claim and Claim Adjustment Expense		19,575	19,048	19,391
Prior Year Claim and Claim Adjustment Expense		(845)	(981)	(937)
Net Losses and Loss Expenses Incurred Related to Prior Year	[1]	(845)	(981)	(937)
Amortization of Deferred Policy Acquisition Costs		5,831	5,630	5,519
Net Paid Losses and Loss Expenses		18,473	18,340	17,448
Net Premiums Written		$ 31,126	$ 29,505	$ 28,225

[1] Relates to prior period loss reserve development only and excludes prior period development related to reinstatement premiums, expense adjustments and earned premiums totaling $53 million, $85 million and $108 million for 2019, 2018, and 2017, respectively.