Decommissioning Trust Funds (Narrative) (Details) (USD $)	3 Months Ended
Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2011
Decommissioning Trust Funds [Abstract]
Deferred taxes on unrealized gains/(losses) recorded in OCI for non-regulated decommissioning trusts	$ 199,000,000	$ 149,000,000
Amortized cost of debt securities	1,589,000,000	1,530,000,000
Average coupon rate of debt securities	4.06%
Average duration of debt securities, years	5.30
Average maturity of debt securities, years	8.43
Proceeds from the dispositions of debt securities	536,000,000.00		493,000,000.00
Gains from dispositions of debt securities, gross	12,000,000.00		4,000,000.00
Losses from dispositions of debt securities, gross	$ 2,000,000		$ 5,000,000

This item represents the total of all debt securities grouped by maturity dates, at cost, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments, as defined), and fair value hedge accounting adjustments, if any, which are classified neither as held-to-maturity nor trading securities.

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This item represents the tax effects occurring during the period which are related to the net unrealized gain (loss) resulting from changes in the fair [carrying] value during the period of available-for-sale securities. Such tax affects would have been charged or credited directly to other comprehensive income or to related components of shareholders' equity.

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- Definition

The cash inflow associated with the sale of debt securities classified as available-for-sale securities.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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