Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Statement of Financial Position [Abstract]
Accumulated depreciation	$ 19,233	$ 19,085
Common stock, par value	$ 0.30	$ 0.30
Common stock, shares authorized	1,800,000,000	1,800,000,000
Common stock, shares issued	1,007,234,000	1,020,057,000
Common stock held in treasury, shares	87,041,000	87,041,000