Accounts Receivable - Changes in Allowance for Fee-for-Service Commissions (Details) $ in Millions	3 Months Ended
	Mar. 31, 2022 USD ($)
Accounts Notes And Loans Receivable [Line Items]
Balance as of December 31, 2021	$ 39
Balance at March 31, 2022	46
Fee-for-Service Commission
Accounts Notes And Loans Receivable [Line Items]
Balance as of December 31, 2021	18
Current period provision for expected credit losses	2
Write-offs charged against the allowance	(8)
Balance at March 31, 2022	$ 12