Available-For-Sale Securities (Value Of Securities That Have Been In An Unrealized Loss Position For Less Than And Greater Than 12 Months) (Details) (USD $) In Millions	Sep. 30, 2011		Dec. 31, 2010
Unrealized Loss Position Greater Than 12 Months [Member] | Total Available-For-Sale Securities Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	$ 8		$ 9
Gross Unrealized Losses	(1)		(1)
Unrealized Loss Position Greater Than 12 Months [Member] | Debt Securities Total [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	8		9
Gross Unrealized Losses	(1)		(1)
Unrealized Loss Position Greater Than 12 Months [Member] | Other Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	6	[1]	8	[1]
Gross Unrealized Losses	(1)	[1]	(1)	[1]
Unrealized Loss Position Greater Than 12 Months [Member] | US States And Political Subdivisions Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	2	[2]	1	[2]
Gross Unrealized Losses	0	[2]	0	[2]
Unrealized Loss Position Greater Than 12 Months [Member] | Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	0	[3]	0	[3]
Gross Unrealized Losses	0	[3]	0	[3]
Unrealized Loss Position Greater Than 12 Months [Member] | Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	0		0
Gross Unrealized Losses	0		0
Unrealized Loss Position Less Than 12 Months [Member] | Total Available-For-Sale Securities Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	390		226
Gross Unrealized Losses	(58)		(8)
Unrealized Loss Position Less Than 12 Months [Member] | Debt Securities Total [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	137		171
Gross Unrealized Losses	(3)		(5)
Unrealized Loss Position Less Than 12 Months [Member] | Other Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	65	[1]	65	[1]
Gross Unrealized Losses	(2)	[1]	(1)	[1]
Unrealized Loss Position Less Than 12 Months [Member] | US States And Political Subdivisions Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	72	[2]	106	[2]
Gross Unrealized Losses	(1)	[2]	(4)	[2]
Unrealized Loss Position Less Than 12 Months [Member] | Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	252	[3]	55	[3]
Gross Unrealized Losses	(55)	[3]	(3)	[3]
Unrealized Loss Position Less Than 12 Months [Member] | Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	1		0
Gross Unrealized Losses	0		0
Total Available-For-Sale Securities Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	170		160
Gross Unrealized Losses	0		0
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	152		142
Gross Unrealized Losses	0		0
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	18		18
Gross Unrealized Losses	$ 0		$ 0

[1] Debt Securities (Corporate)—Power's investments in corporate bonds are primarily in investment grade securities. It is not expected that these securities would settle for less than their amortized cost. Since Power does not intend to sell these securities nor will it be more-likely-than-not required to sell, Power does not consider these debt securities to be other-than-temporarily impaired as of September 30, 2011.

[2] Debt Securities (Government)—Unrealized losses on Power's NDT investments in United States Treasury obligations and Federal Agency mortgage-backed securities were caused by interest rate changes. Since these investments are guaranteed by the United States government or an agency of the United States government, it is not expected that these securities will settle for less than their amortized cost basis, since Power does not intend to sell nor will it be more-likely-than-not required to sell. Power does not consider these securities to be other-than-temporarily impaired as of September 30, 2011.

[3] Equity Securities—Investments in marketable equity securities within the NDT funds are primarily investments in common stocks within a broad range of industries and sectors. The unrealized losses are distributed over hundreds of companies with limited impairment durations. Power does not consider these securities to be other-than-temporarily impaired as of September 30, 2011.