Schedule V - Supplemental Information Concerning Property and Casualty Insurance Operations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Supplemental Information Concerning Property and Casualty Insurance Operations [Abstract]
Deferred acquisition costs	$ 708	$ 662
Reserves for unpaid claim and claim adjustment expenses	22,706	21,720
Discount deducted from claim and claim adjustment expense reserves above (based on interest rates ranging from 3.5% to 6.5%)	1,209	1,321
Unearned premiums	5,119	4,583
Net written premiums	8,059	7,656	$ 7,345
Net earned premiums	7,649	7,428	7,312
Net investment income	1,896	2,063	1,751
Incurred claim and claim adjustment expenses related to current year	5,793	5,356	5,358
Incurred claim and claim adjustment expenses related to prior years	(119)	(127)	(179)
Amortization of deferred acquisition costs	1,410	1,383	1,335
Paid claim and claim adjustment expenses	$ 5,164	$ 5,576	$ 5,331
Minimum [Member]
Supplemental Information Concerning Property and Casualty Insurance Operations [Abstract]
Interest rate at which discount computed	3.50%	3.50%
Maximum [Member]
Supplemental Information Concerning Property and Casualty Insurance Operations [Abstract]
Interest rate at which discount computed	6.50%	6.50%