Other Investments (Tables)

3 Months Ended

Mar. 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:

		Amortized Cost				Fair Value
(in millions)	Longest Maturity Dates	March 31, 2012		December 31, 2011		March 31, 2012		December 31, 2011
Stocks	—	$	885	$	865	$	2,124	$	1,899
Municipal bonds	2051	574		625		696		756
U.S. government and agency securities	2041	596		516		642		580
Corporate bonds	2054	305		259		369		317
Short-term investments and receivables/payables	One-year	21		38		22		40
Total		$	2,381	$	2,303	$	3,853	$	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:

	Three months ended March 31,
(in millions)	2012			2011
Balance at beginning of period	$	3,592		$	3,480
Gross realized gains	25			23
Gross realized losses	(4		)	—
Unrealized gains (losses) – net	184			102
Other-than-temporary impairments	(5		)	(9		)
Interest, dividends, contributions and other	61			23
Balance at end of period	$	3,853		$	3,619