Accrued Workers' Compensation Cost - Additional Information (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Financial Guarantee Insurance Contracts, Claim Liability [Line Items]
Collateral held by insurance carriers	$ 55	$ 57
Liability For Unpaid Claims And Claims Adjustment Expense, Collateral	$ 12	$ 13

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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