Consolidated Balance Sheets (Unaudited) (Parentheticals) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Current Assets:
Allowance for uncollectible accounts	$ 13	$ 12
Allowance for obsolescence	119	113
Property and Equipment, Net:
Accumulated depreciation and amortization	14,585	14,097
Other Assets:
Accumulated amortization of identifiable intangibles	$ 849	$ 845
Stockholders' Equity:
Common stock, par value (in USD per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized	1,500,000,000	1,500,000,000
Common stock, shares issued	710,603,639	714,674,160
Treasury stock, at cost, shares	8,125,434	7,476,181