Consolidated Balance Sheets (Unaudited) (Parentheticals) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Current Assets:
Allowance for uncollectible accounts	$ 14	$ 12
Allowance for obsolescence	94	102
Noncurrent Assets:
Accumulated depreciation and amortization	17,213	15,823
Accumulated amortization	$ 871	$ 862
Stockholders' Equity:
Common stock, par value (USD per share)	$ 0.0001	$ 0.0001
Common stock, authorized (shares)	1,500,000,000	1,500,000,000
Common stock, issued (shares)	655,694,564	688,136,306
Treasury stock, at cost (shares)	8,951,710	8,191,831

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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The amount of the valuation account as of the balance sheet date which reduces the carrying amount of airline related inventory (including expendable merchandise, goods, commodities, or supplies to be used primarily in air transport of passengers or freight) to net realizable value; takes into consideration such factors as market value, excessive quantities based on expected sales, technological obsolescence, and shrinkage.

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