Financial Instruments (Debt) (Narrative) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Fair Value, Inputs, Level 2 [Member]
Fair value of debt	$ 14,460	$ 13,015
2.80% notes due February 15, 2023 [Member]
Senior notes	1,250
Senior Note 2 Point 80 Due February 15, 2023 [Member]
Debt Instrument, Interest Rate, Stated Percentage	2.80%
4.15% notes due February 15, 2043 [Member]
Senior notes	$ 750
Senior Note 4 Point 15 Due February 15, 2043 [Member]
Debt Instrument, Interest Rate, Stated Percentage	4.15%