Significant Financing Transactions - (Commercial Paper, Bank Loans and Letters of Credit Outstanding) (Details) (USD $) In Millions	9 Months Ended
	Sep. 30, 2011
Facility Limit	$ 3,500
Outstanding Commercial Paper	783
Outstanding Letters of Credit	127
Facility Capacity Available	2,590
Credit Facility, to support letters of credit	1,500
Credit Facility 1.5 Billion [Member] | Three Year Joint Revolving Credit Facility [Member}
Facility Limit	3,000	[1]
Outstanding Commercial Paper	783	[1]
Outstanding Letters of Credit	0	[1]
Facility Capacity Available	2,217	[1]
Credit facility initiation date	September 2010
Credit facility termination date	September 2016
Three Year Joint Revolving Credit Facility [Member}
Facility Limit	500	[2]
Outstanding Commercial Paper	0	[2]
Outstanding Letters of Credit	127	[2]
Facility Capacity Available	$ 373	[2]
Credit facility initiation date	September 2010
Credit facility termination date	September 2016

[1] This credit facility was entered into in September 2010 with an original maturity date of September 2013. Effective October 1, 2011, pricing was amended and the maturity date was extended to September 2016. This credit facility can be used to support bank borrowings and the issuance of commercial paper, as well as to support up to $1.5 billion of letters of credit.

[2] This credit facility was entered into in September 2010 with an original maturity date of September 2013. Effective October 1, 2011, pricing was amended and the maturity date was extended to September 2016. This credit facility can be used to support bank borrowings, commercial paper and letter of credit issuances.