Acquisitions and Dispositions (Discontinued Operations) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2016 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income From Discontinued Operations, net of tax	$ 122
International Energy [Member] | Discontinued Operations, Disposed of by Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Operating Revenues	246
Fuel used in electric generation and purchased power	47
Cost of natural gas	11
Operation, maintenance and other	71
Deprecation and amortization	22
Property and other taxes	3
Other Income and Expenses, net	10
Interest Expense	22
Income before income taxes	80
Income tax benefit	(39)
Income From Discontinued Operations, net of tax	119
Other Disposal Groups [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income From Discontinued Operations, net of tax	3
Previously Remitted Earnings [Member] | International Energy [Member] | Discontinued Operations, Disposed of by Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income tax benefit	$ (95)