Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 157	$ 185
Accumulated depreciation	6,825	6,055
Finite-lived intangible assets, accumulated amortization	$ 476	$ 387
Common stock, par value (USD per share)	$ 1	$ 1
Common stock, shares authorized (in shares)	250,000,000	250,000,000
Common stock, shares issued (in shares)	112,000,000	111,000,000
Common stock, shares outstanding (in shares)	71,000,000	74,000,000
Treasury stock shares (in shares)	41,000,000	37,000,000