Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Receivables, allowances	$ 30	$ 42
Common stock, no par value (in dollars per share)
Common stock, shares issued (in shares)	2,109,316,331	2,109,316,331
Repurchased stock, shares (in shares)	556,098,569	557,930,784