Consolidated Balance Sheets (Parenthetical) - USD ($) shares in Millions, $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Allowance for bad debt	$ 175	$ 145
Accumulated depreciation	$ 11,198	$ 11,576
Shareholders’ equity:
Common stock, par value (in dollars per share)	$ 2.50	$ 2.50
Common stock, shares authorized (in shares)	2,000	2,000
Common stock, shares issued (in shares)	1,070	1,071
Treasury shares (in shares)	204	215