DESCRIPTION OF BUSINESS AND SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)	12 Months Ended
	Dec. 31, 2023 USD ($) reporting_unit segment	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Summary Of Significant Accounting Policy [Line Items]
Number of reportable segments | segment	1
Advance collection	$ 8,000,000	$ 9,000,000
Maximum reimbursement per claim occurrence	$ 1,000,000
Plan years to be settled	10 years
Prepayments and miscellaneous receivables offsetting accrued health insurance costs	$ 58,000,000	$ 57,000,000
Weighted-average rate used in discounting the lease liabilities	4.20%	3.90%
Number of reporting units | reporting_unit	1
Impairment of goodwill	$ 0	$ 0	$ 0
Advertising costs	37,000,000	29,000,000	21,000,000
Bad debt expense, net of recoveries	$ 3,000,000	2,000,000	$ 0
Minimum
Summary Of Significant Accounting Policy [Line Items]
Estimated useful life of intangible assets	1 year
Minimum | Software Development
Summary Of Significant Accounting Policy [Line Items]
Estimated useful life of intangible assets	3 years
Minimum | Furniture, fixtures, and equipment
Summary Of Significant Accounting Policy [Line Items]
Estimated useful life of property and equipment	5 years
Minimum | Office equipment, including data processing equipment
Summary Of Significant Accounting Policy [Line Items]
Estimated useful life of property and equipment	5 years
Maximum
Summary Of Significant Accounting Policy [Line Items]
Estimated useful life of intangible assets	10 years
Maximum | Software Development
Summary Of Significant Accounting Policy [Line Items]
Estimated useful life of intangible assets	6 years
Maximum | Furniture, fixtures, and equipment
Summary Of Significant Accounting Policy [Line Items]
Estimated useful life of property and equipment	7 years
Maximum | Office equipment, including data processing equipment
Summary Of Significant Accounting Policy [Line Items]
Estimated useful life of property and equipment	7 years
Health Care
Summary Of Significant Accounting Policy [Line Items]
Prepayments and miscellaneous receivables offsetting accrued health insurance costs	$ 68,000,000	$ 73,000,000
Non-US | Geographic Concentration Risk | Revenue
Summary Of Significant Accounting Policy [Line Items]
Concentration risk percentage	1.00%