Financial Instruments (Narative) (Details) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Financial Instruments, Owned, at Fair Value [Abstract]
Short-term investments	$ 1,849,000,000	$ 150,000,000
Marketable equity securities	45,000,000	43,000,000
Fair Value, Liabilities, Level 2 to Level 1 Transfers, Amount	$ 2,000,000,000