Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) (USD $) In Millions, except Per Share data, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Current assets:
Allowance for bad debts	$ 96	$ 92
Accumulated depreciation	$ 9,137	$ 8,056
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)	1,072	1,073
Treasury shares (in shares)	225	144