Financing (Details 2) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Short-term borrowings
Short-term Debt at the End of the Period, Amount Outstanding	$ 854
Short-term Debt at the End of the Period, Weighted Average Interest Rate	0.49%
Short-term Debt During the Period, Average Outstanding	711
Short-term Debt During the Period, Weighted Average Interest Rate	0.32%
Commercial paper [Member]
Short-term borrowings
Short-term Debt at the End of the Period, Amount Outstanding	654	1,295
Short-term Debt at the End of the Period, Weighted Average Interest Rate	0.28%	0.32%
Short-term Debt During the Period, Average Outstanding	697	690
Short-term Debt During the Period, Weighted Average Interest Rate	0.29%	0.29%
Short-term Debt During the Period, Maximum Amount Outstanding	1,586	1,305
Short-term bank debt [Member]
Short-term borrowings
Short-term Debt at the End of the Period, Amount Outstanding	200
Short-term Debt at the End of the Period, Weighted Average Interest Rate	1.18%
Short-term Debt During the Period, Average Outstanding	14
Short-term Debt During the Period, Weighted Average Interest Rate	1.21%
Short-term Debt During the Period, Maximum Amount Outstanding	$ 200