Schedule II - Valuation Accounts and Reserves (Details) - Allowance for Doubtful Accounts [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balance	$ 250	$ 236	$ 236
Provision for doubtfull accounts	297	296	270
Net deductions and other	293	282	270
Ending balance	$ 254	$ 250	$ 236