Accumulated Other Comprehensive Income (Loss) (Income (Expense) Effect of Reclassifications) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Affected Line Item on the Statements of Income [Line Items]
Unregulated wholesale energy	$ 521	$ (1,457)
Energy purchases	(321)	1,494
Depreciation	(293)	(300)
Other Income (Expense) - net	95	(23)
Interest Expense	(247)	(262)
Total Pre-tax	915	438
Income Taxes	(268)	(114)
Total After-Tax	647	324
Amounts Reclassified From Accumulated Other Comprehensive Income [Member]
Affected Line Item on the Statements of Income [Line Items]
Total After-Tax	(19)	(46)
Available For Sale Securities [Member] | Amounts Reclassified From Accumulated Other Comprehensive Income [Member]
Affected Line Item on the Statements of Income [Line Items]
Other Income (Expense) - net	2	2
Total Pre-tax	2	2
Income Taxes	(1)	(1)
Total After-Tax	1	1
Qualifying Derivatives [Member] | Amounts Reclassified From Accumulated Other Comprehensive Income [Member]
Affected Line Item on the Statements of Income [Line Items]
Total Pre-tax	21	(23)
Income Taxes	(4)	4
Total After-Tax	17	(19)
Qualifying Derivatives [Member] | Interest Rate Swaps [Member] | Amounts Reclassified From Accumulated Other Comprehensive Income [Member]
Affected Line Item on the Statements of Income [Line Items]
Interest Expense	(4)	(3)
Qualifying Derivatives [Member] | Cross Currency Swaps [Member] | Amounts Reclassified From Accumulated Other Comprehensive Income [Member]
Affected Line Item on the Statements of Income [Line Items]
Other Income (Expense) - net	17	(29)
Interest Expense	1	0
Qualifying Derivatives [Member] | Energy Commodities [Member] | Amounts Reclassified From Accumulated Other Comprehensive Income [Member]
Affected Line Item on the Statements of Income [Line Items]
Unregulated wholesale energy	(2)	(1)
Energy purchases	8	7
Discontinued operations	0	2
Other	1	1
Defined Benefit Plans [Member] | Amounts Reclassified From Accumulated Other Comprehensive Income [Member]
Affected Line Item on the Statements of Income [Line Items]
Total Pre-tax	(51)	(38)
Income Taxes	13	10
Total After-Tax	(38)	(28)
Defined Benefit Plans [Member] | Prior Service Costs [Member] | Amounts Reclassified From Accumulated Other Comprehensive Income [Member]
Affected Line Item on the Statements of Income [Line Items]
Total Pre-tax	0	(2)
Defined Benefit Plans [Member] | Net Actuarial Loss [Member] | Amounts Reclassified From Accumulated Other Comprehensive Income [Member]
Affected Line Item on the Statements of Income [Line Items]
Total Pre-tax	(51)	(36)
Equity Investees Accumulated Other Comprehensive Income [Member] | Amounts Reclassified From Accumulated Other Comprehensive Income [Member]
Affected Line Item on the Statements of Income [Line Items]
Other Income (Expense) - net	2	0
Total Pre-tax	2	0
Income Taxes	(1)	0
Total After-Tax	$ 1	$ 0