Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Current Assets:
Allowance for uncollectible accounts	$ 15	$ 9
Allowance for obsolescence	110	114
Property and Equipment, Net:
Accumulated depreciation and amortization	12,456	10,871
Other Assets:
Accumulated amortization	$ 828	$ 811
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	744,886,938	799,850,675
Treasury stock, at cost, shares	14,149,229	21,066,684