Supplemental Financial Statement Information - Additional Information (Details) - USD ($)			9 Months Ended
	Apr. 03, 2020	Mar. 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Effects of Reinsurance [Line Items]
Cash and cash equivalents and short-term investments			$ 2,500,000,000		$ 2,900,000,000
Restricted cash and cash equivalents and restricted short-term investments			1,300,000,000		$ 1,600,000,000
Allowance for credit loss on marketable and non-marketable available for sale debt securities			0
Transfer of certain legacy auto insurance liabilities			407,885,000	$ 0
Loss recognized from net cost of novation agreement			64,700,000
Cost of revenue
Effects of Reinsurance [Line Items]
Loss recognized from net cost of novation agreement			62,500,000
General and administrative
Effects of Reinsurance [Line Items]
Loss recognized from net cost of novation agreement			$ 2,200,000
Clarendon National Insurance Company | Pacific Valley Insurance Company, Inc.
Effects of Reinsurance [Line Items]
Transfer of reinsurance obligations	$ 465,000,000.0	$ 465,000,000.0
Reinsurance obligations		$ 816,000,000.0