Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Allowance for doubtful accounts
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 43	$ 49	$ 64
Charged to Costs and Expenses	32	13	4
Deductions	20	19	19
Balance at End of Period	55	43	49
Reserve for obsolescence and shrinkage
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	3	3	3
Charged to Costs and Expenses	18	18	16
Deductions	17	18	16
Balance at End of Period	4	3	3
Self-insurance reserve
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	92	94	97
Charged to Costs and Expenses	110	105	92
Deductions	112	107	95
Balance at End of Period	$ 90	$ 92	$ 94