Schedule II - Valuation Accounts and Reserves (Details) (Allowance for Doubtful Accounts [Member], 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]
Beginning balance	$ 236		$ 236		$ 237
Provision for doubtfull accounts	296		270		269
Net deductions and other	282	[1]	270	[1]	270	[1]
Ending balance	$ 250		$ 236		$ 236

[1] Primarily represents the write-off of accounts receivable, net of recoveries.