Fair Value Measurements and Credit Concentration (Nonrecurring Fair Value Measurements and Credit Concentration) (Details) (USD $)	Mar. 31, 2012		Dec. 31, 2011
Credit Concentration Associated with Financial Instruments (Numeric) [Abstract]
Gross credit exposure to energy trading partners	$ 3,600,000,000
Net credit exposure to energy trading partners	954,000,000
Dollar exposure to top ten energy trading counterparties	460,000,000
Percentage exposure to top ten energy trading counterparties	48.00%
Carrying Amount [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Contract adjustment payments	175,000,000	[1]	198,000,000	[1]
Long-term debt	18,076,000,000		17,993,000,000
Fair Value [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Contract adjustment payments	176,000,000		198,000,000
Long-term debt	$ 19,837,000,000		$ 19,392,000,000

[1] Reflected in "Other current liabilities" and "Other deferred credits and noncurrent liabilities" on the Balance Sheets.