Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2022	Dec. 31, 2021
Current Assets:
Allowance for uncollectible accounts	$ 41	$ 50
Allowance for obsolescence	152	176
Noncurrent Assets:
Accumulated depreciation and amortization	19,338	18,671
Accumulated amortization	$ 897	$ 893
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)	651,700,403	649,720,387
Treasury stock, at cost (shares)	10,502,485	9,752,872