Accrued Workers' Compensation Cost - Summary of Workers' Compensation Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Insurance [Abstract]
Total accrued costs, end of period	$ 217	$ 214	$ 236	$ 238
Collateral paid to carriers and offset against accrued costs	(9)	(9)
Total accrued costs, net of carrier collateral offset	208	205
Payable in less than 1 year (net of collateral paid to carriers of $3 at March 31, 2020 and December 31, 2019)	63	61
Payable in more than 1 year (net of collateral paid to carriers of $6 at March 31, 2020 and December 31, 2019)	145	144
Accrued health insurance costs, net current	3	3
Accrued health insurance costs, net noncurrent	$ 6	$ 6