Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Allowance for doubtful accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balance	$ 103	$ 93	$ 68
Acquired	0	2	14
Charged to costs and expenses	9	8	45
Charged to revenue	25	34	0
Deductions	29	34	34
Ending balance	108	103	93
Reserve for obsolescence and shrinkage
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balance	10	5	7
Acquired	0	4	1
Charged to costs and expenses	34	40	26
Charged to revenue	0	0	0
Deductions	36	39	29
Ending balance	8	10	5
Self-insurance reserve
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balance	121	106	100
Acquired	0	0	5
Charged to costs and expenses	169	180	144
Charged to revenue	0	0	0
Deductions	163	165	143
Ending balance	$ 127	$ 121	$ 106