Other Investments (Tables)

12 Months Ended

Dec. 31, 2011

Regulated Entity, Other Assets, Noncurrent [Abstract]

Amortized cost and fair value of the trust investments:

The following table sets forth amortized cost and fair value of the trust investments:

		Amortized Cost				Fair Value
(in millions)	Longest Maturity Dates	December 31, 2011		December 31, 2010		December 31, 2011		December 31, 2010
Stocks	—	$	865	$	895	$	1,899	$	2,029
Municipal bonds	2051	625		706		756		790
U.S. government and agency securities	2041	516		270		580		288
Corporate bonds	2054	259		288		317		346
Short-term investments and receivables/payables	One-year	38		26		40		27
Total		$	2,303	$	2,185	$	3,592	$	3,480

Summary of changes in the fair value of trust

The following table sets forth a summary of changes in the fair value of the trust for the years ended December 31:

(in millions)	2011			2010			2009
Balance at beginning of period	$	3,480		$	3,140		$	2,524
Gross realized gains	108			125			242
Gross realized losses	(17		)	(4		)	(147		)
Unrealized gains (losses) – net	(7		)	148			526
Other-than-temporary impairments	(47		)	(27		)	(111		)
Interest, dividends, contributions and other	75			98			106
Balance at end of period	$	3,592		$	3,480		$	3,140