Reinsurance and Indemnification - Michigan Catastrophic Claims Association (Details) - USD ($)	6 Months Ended	12 Months Ended	24 Months Ended
	Jun. 30, 2019	Dec. 31, 2019	Jun. 30, 2021	Jun. 30, 2019	Dec. 31, 2018
Reinsurance Retention Policy [Line Items]
Assets		$ 119,950,000,000			$ 112,249,000,000
Retained income		48,074,000,000			44,033,000,000
Michigan Catastrophic Claim Association
Reinsurance Retention Policy [Line Items]
Reinsurance and indemnification recoverables, net		5,500,000,000			$ 5,400,000,000
Program funding, per vehicle annual assessment		$ 220
Reinsurance increase, percentage		6.00%
Retention level per claim				$ 555,000
Assets	$ 21,830,000,000			21,830,000,000
Retained income	1,280,000,000			$ 1,280,000,000
Retained earnings accumulated deficit decrease	$ (39,640,000,000)
Subsequent Event | Michigan Catastrophic Claim Association
Reinsurance Retention Policy [Line Items]
Retention level per claim			$ 580,000
Term of catastrophe reinsurance agreement contract			2 years