Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) shares in Millions, $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Current assets:
Allowance for bad debts	$ 138	$ 137
Accumulated depreciation	$ 9,540	$ 11,007
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)	1,071	1,071
Treasury shares (in shares)	216	223