Cash, Cash Equivalents and Investments - Additional Information (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 563	$ 213
Investments	61	68
Restricted cash, cash equivalents and investments	832	1,180
Investments, noncurrent	141	125
Restricted cash, cash equivalents and investments, noncurrent	205	212
Total cash equivalents and investments and restricted cash equivalents and investments	1,802	1,798
Cash and cash equivalents
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	563	213
Investments	0	0
Restricted cash, cash equivalents and investments	744	1,180
Investments, noncurrent	0	0
Total cash equivalents and investments and restricted cash equivalents and investments	1,342	1,456
Available-for-sale marketable securities
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	0	0
Investments	61	68
Restricted cash, cash equivalents and investments	88	0
Investments, noncurrent	141	125
Total cash equivalents and investments and restricted cash equivalents and investments	460	341
Certificate of deposits
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents		0
Investments		0
Restricted cash, cash equivalents and investments		0
Investments, noncurrent		0
Total cash equivalents and investments and restricted cash equivalents and investments		1
Payroll funds collected
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash, cash equivalents and investments	664	1,018
Payroll funds collected \| Cash and cash equivalents
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash, cash equivalents and investments	664	1,018
Payroll funds collected \| Available-for-sale marketable securities
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash, cash equivalents and investments	0	0
Payroll funds collected \| Certificate of deposits
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash, cash equivalents and investments		0
Collateral for health benefits claims
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash, cash equivalents and investments	104	98
Collateral for health benefits claims \| Cash and cash equivalents
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash, cash equivalents and investments	16	98
Collateral for health benefits claims \| Available-for-sale marketable securities
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash, cash equivalents and investments	88	0
Collateral for health benefits claims \| Certificate of deposits
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash, cash equivalents and investments		0
Collateral for workers' compensation claims
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash, cash equivalents and investments	62	62
Restricted cash, cash equivalents and investments, noncurrent	205	212
Collateral for workers' compensation claims \| Cash and cash equivalents
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash, cash equivalents and investments	62	62
Restricted cash, cash equivalents and investments, noncurrent	35	63
Collateral for workers' compensation claims \| Available-for-sale marketable securities
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash, cash equivalents and investments	0	0
Restricted cash, cash equivalents and investments, noncurrent	170	148
Collateral for workers' compensation claims \| Certificate of deposits
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash, cash equivalents and investments		0
Restricted cash, cash equivalents and investments, noncurrent		1
Other security deposits
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash, cash equivalents and investments	2	2
Other security deposits \| Cash and cash equivalents
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash, cash equivalents and investments	2	2
Other security deposits \| Available-for-sale marketable securities
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash, cash equivalents and investments	$ 0	0
Other security deposits \| Certificate of deposits
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash, cash equivalents and investments		$ 0

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), classified as noncurrent.

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Cash and investments whose use in whole or in part is restricted for the long-term, generally by contractual agreements or regulatory requirements. For use in an unclassified balance sheet.

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The noncurrent cash, cash equivalents and investments that is restricted as to withdrawal or usage. Restrictions may include legally restricted deposits held as compensating balances against borrowing arrangements, contracts entered into with others, or entity statements of intention with regard to particular deposits classified as long-term; that is not expected to be released from such existing restrictions within one year of the balance sheet date or operating cycle, whichever is longer. Excludes compensating balance arrangements that are not agreements which legally restrict the use of cash amounts shown on the balance sheet. Includes noncurrent cash equivalents and investments that are similarly restricted as to withdrawal, usage or disposal.

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Amount of investments including trading securities, available-for-sale securities, held-to-maturity securities, and short-term investments classified as other and current.

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