Schedule II - Valuation and Qualifying Accounts (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Allowance for doubtful accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 49		$ 64		$ 33
Acquired	0		0		13
Charged to Costs and Expenses	13		4		37
Deductions	19	[1]	19	[1]	19	[1]
Balance at End of Period	43		49		64
Reserve for obsolescence and shrinkage [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	3		3		2
Acquired	0		0		1
Charged to Costs and Expenses	18		16		13
Deductions	18	[2]	16	[2]	13	[2]
Balance at End of Period	3		3		3
Self-insurance reserve [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	94		97		83
Acquired	0		0		21
Charged to Costs and Expenses	105		92		84
Deductions	107	[3]	95	[3]	91	[3]
Balance at End of Period	$ 92		$ 94		$ 97

[1] Represents write-offs of accounts, net of recoveries.

[2] Represents write-offs.

[3] Represents payments.