Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Allowance for doubtful accounts
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 55	$ 43	$ 49
Charged to Costs and Expenses	24	32	13
Deductions	25	20	19
Balance at End of Period	54	55	43
Reserve for obsolescence and shrinkage
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	4	3	3
Charged to Costs and Expenses	17	18	18
Deductions	18	17	18
Balance at End of Period	3	4	3
Self-insurance reserve
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	90	92	94
Charged to Costs and Expenses	108	110	105
Deductions	104	112	107
Balance at End of Period	$ 94	$ 90	$ 92