Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Current Assets:
Allowance for uncollectible accounts	$ 12	$ 15
Allowance for obsolescence	113	110
Property and Equipment, Net:
Accumulated depreciation and amortization	14,097	12,456
Other Assets:
Accumulated amortization	$ 845	$ 828
Stockholders' Equity:
Common stock, par value (usd per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized	1,500,000,000	1,500,000,000
Common stock, shares issued	714,674,160	744,886,938
Treasury stock, at cost, shares	7,476,181	14,149,229