MARKETABLE SECURITIES (Tables)

6 Months Ended

Jun. 30, 2011

Notes To Consolidated Financial Statements [Abstract]

Schedule Of Available For Sale Securities Reconciliation [Table TextBlock]

		As of June 30, 2011
				Pre-Tax		Pre-Tax
		Amortized		Unrealized		Unrealized
(Millions of Dollars)		Cost		Gains(1)		Losses(1)		Fair Value
NU
U.S. Government Issued Debt Securities
	(Agency and Treasury)	$	13.1	$	0.3	$	-	$	13.4
Corporate Debt Securities			12.6		0.5		-		13.1
Asset Backed Debt Securities			9.4		0.4		(0.1)		9.7
Municipal Bonds			26.4		0.1		-		26.5
Money Market Funds and Other			25.5		0.2		-		25.7
Total NU		$	87.0	$	1.5	$	(0.1)	$	88.4
WMECO Spent Nuclear Fuel Trust
Corporate Debt Securities		$	5.9	$	-	$	-	$	5.9
Asset Backed Debt Securities			3.1		-		(0.1)		3.0
Municipal Bonds			25.8		-		-		25.8
Money Market Funds and Other			22.4		-		-		22.4
Total WMECO Spent Nuclear Fuel Trust		$	57.2	$	-	$	(0.1)	$	57.1

		As of December 31, 2010
				Pre-Tax		Pre-Tax
		Amortized		Unrealized		Unrealized
(Millions of Dollars)		Cost		Gains(1)		Losses(1)		Fair Value
NU
U.S. Government Issued Debt Securities
	(Agency and Treasury)	$	17.7	$	0.2	$	(0.1)	$	17.8
Corporate Debt Securities			22.1		0.5		(0.1)		22.5
Asset Backed Debt Securities			11.3		0.4		(0.1)		11.6
Municipal Bonds			16.1		-		-		16.1
Money Market Funds and Other			19.1		0.2		-		19.3
Total NU		$	86.3	$	1.3	$	(0.3)	$	87.3
WMECO Spent Nuclear Fuel Trust
U.S. Government Issued Debt Securities
	(Agency and Treasury)	$	6.0	$	-	$	-	$	6.0
Corporate Debt Securities			15.6		-		-		15.6
Asset Backed Debt Securities			4.8		-		(0.1)		4.7
Municipal Bonds			15.4		-		-		15.4
Money Market Funds and Other			15.4		-		-		15.4
Total WMECO Spent Nuclear Fuel Trust		$	57.2	$	-	$	(0.1)	$	57.1

Investments Classified by Contractual Maturity Date [Table Text Block]

	NU				WMECO
	Amortized				Amortized
(Millions of Dollars)	Cost		Fair Value		Cost		Fair Value
Less than one year	$	30.2	$	30.3	$	28.0	$	28.0
One to five years		12.3		12.5		6.7		6.8
Six to ten years		6.3		6.7		2.0		1.9
Greater than ten years		38.2		38.9		20.5		20.4
Total Debt Securities	$	87.0	$	88.4	$	57.2	$	57.1

Fair Value Heirarchy [Table Text Block]

			NU				WMECO
			As of		As of		As of		As of
(Millions of Dollars)			June 30, 2011		December 31, 2010		June 30, 2011		December 31, 2010
Level 1:
	Mutual Funds		$	44.4	$	42.2	$	-	$	-
	Money Market Funds			2.1		1.8		1.1		0.3
Total Level 1			$	46.5	$	44.0	$	1.1	$	0.3
Level 2:
	U.S. Government Issued Debt Securities
		(Agency and Treasury)		13.4		17.8		-		6.0
	Corporate Debt Securities			13.1		22.5		5.9		15.6
	Asset Backed Debt Securities			9.7		11.6		3.0		4.7
	Municipal Bonds			26.5		16.1		25.8		15.4
	Other Fixed Income Securities			23.6		17.5		21.3		15.1
Total Level 2			$	86.3	$	85.5	$	56.0	$	56.8
Total Marketable Securities			$	132.8	$	129.5	$	57.1	$	57.1