Other Investments (Tables)

12 Months Ended

Dec. 31, 2012

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:

	Longest Maturity	Amortized Cost				Fair Value
		December 31,
(in millions)	Dates	2012		2011		2012		2011
Stocks	—	$	978	$	865	$	2,271	$	1,899
Municipal bonds	2054	518		625		644		756
U.S. government and agency securities	2043	547		516		603		580
Corporate bonds	2054	324		259		410		317
Short-term investments and receivables/payables	One-year	116		38		120		40
Total		$	2,483	$	2,303	$	4,048	$	3,592

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:

	Years ended December 31,
(in millions)	2012			2011			2010
Balance at beginning of period	$	3,592		$	3,480		$	3,140
Gross realized gains	73			108			125
Gross realized losses	(5		)	(17		)	(4		)
Unrealized gains (losses), net	276			(7		)	148
Other-than-temporary impairments	(36		)	(47		)	(27		)
Interest, dividends, contributions and other	148			75			98
Balance at end of period	$	4,048		$	3,592		$	3,480