Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Statement Of Financial Position [Abstract]
Allowance for Accounts Receivable	$ 144	$ 150
Accumulated Depreciation	$ 10,935	$ 10,991
Common Stock, par value (in dollars per share)	$ 0	$ 0
Common Stock, shares authorized (in shares)	450,000,000	450,000,000
Common Stock, shares outstanding (in shares)	235,000,000	233,000,000