Supplemental Financial Statement Information - Additional Information (Details) - USD ($)			3 Months Ended
	Apr. 03, 2020	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Effects of Reinsurance
Cash and cash equivalents and short-term investments			$ 2,200,000,000		$ 2,300,000,000
Restricted cash and cash equivalents and restricted short-term investments			1,100,000,000		1,200,000,000
Allowance for credit loss on marketable and non-marketable available for sale debt securities			0
Transfer of certain legacy auto insurance liabilities			0	$ 407,885,000
Loss recognized from net cost of novation agreement				64,700,000
Cash and Cash Equivalents and Short-Term Investments
Effects of Reinsurance
Cash			44,200,000		133,600,000
Restricted Cash and Cash Equivalents and Restricted Investments
Effects of Reinsurance
Restricted cash			$ 57,000,000.0		$ 53,800,000
Cost of revenue
Effects of Reinsurance
Loss recognized from net cost of novation agreement				62,500,000
General and administrative
Effects of Reinsurance
Loss recognized from net cost of novation agreement				2,200,000
Clarendon National Insurance Company | Pacific Valley Insurance Company, Inc.
Effects of Reinsurance
Transfer of reinsurance obligations	$ 465,000,000.0	$ 465,000,000.0
Reinsurance obligations		$ 816,000,000.0		$ 816,000,000.0