Reinsurance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Reinsurance Disclosures [Abstract]
Percentage of residual market business written directly by the Company for mandatory pools and associations and then ceded to the mandatory pool	100.00%
Written premiums, direct	$ 33,180	$ 30,762	$ 30,022
Written premiums, assumed	1,064	1,001	1,041
Written premiums, ceded	(2,285)	(2,031)	(1,912)
Total net written premiums	31,959	29,732	29,151
Earned premiums, direct	31,977	29,978	28,994
Earned premiums, assumed	1,032	1,010	1,076
Earned premiums, ceded	(2,154)	(1,944)	(1,798)
Total net earned premiums	$ 30,855	$ 29,044	$ 28,272
Percentage of assumed earned premiums to net earned premiums	3.30%	3.50%	3.80%
Ceded claims and claim adjustment expenses incurred	$ 1,184	$ 1,030	$ 1,089
Gross reinsurance recoverables on paid and unpaid claims and claim adjustment expenses excluding structured settlements and mandatory pools and associations	3,931	3,731
Gross structured settlements	2,900	2,964
Mandatory pools and associations	1,762	1,801
Gross reinsurance recoverables	8,593	8,496
Allowance for uncollectible reinsurance	(141)	(146)	(92)
Net reinsurance recoverables	8,452	$ 8,350	$ 8,235
Terrorism Risk Insurance Program, annual aggregate industry loss minimum in order for a loss to be covered	$ 200
Terrorism Risk Insurance Program, percentage of subject losses reimbursed by the Federal Government, after insurer deductible, subject to annual cap	80.00%
Terrorism Risk Insurance Program, percentage of insurer's direct earned premiums for covered lines for the preceding calendar year at which the deductible is set	20.00%
Terrorism Risk Insurance Program, Company's estimated deductible for the next fiscal year	$ 2,710
Terrorism Risk Insurance Program, annual cap limiting amount of aggregate subject losses for all participating insurers	100,000
Terrorism Risk Insurance Program, terrorism-related losses triggering program coverage since program was established	$ 0