MARKETABLE SECURITIES (Tables)

12 Months Ended

Dec. 31, 2011

Notes To Consolidated Financial Statements [Abstract]

Schedule Of Available For Sale Securities Reconciliation [Table TextBlock]

	As of December 31, 2011
			Pre-Tax		Pre-Tax
	Amortized		Unrealized		Unrealized
	Cost		Gains(1)		Losses(1)		Fair Value
(Millions of Dollars)
NU	$	88.4	$	2.0	$	(0.2)	$	90.2
WMECO		57.3		-		(0.2)		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	$	86.3	$	1.3	$	(0.3)	$	87.3
WMECO		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	$	29.9	$	29.9	$	26.4	$	26.3
One to five years		25.4		25.6		20.7		20.7
Six to ten years		10.9		11.3		6.1		6.1
Greater than ten years		22.2		23.4		4.1		4.0
Total Debt Securities	$	88.4	$	90.2	$	57.3	$	57.1

Fair Value Heirarchy [Table Text Block]

			NU				WMECO
			As of December 31,				As of December 31,
(Millions of Dollars)			2011		2010		2011		2010
Level 1:
	Mutual Funds		$	41.1	$	42.2	$	-	$	-
	Money Market Funds			1.8		1.8		0.1		0.3
Total Level 1			$	42.9	$	44.0	$	0.1	$	0.3
Level 2:
	U.S. Government Issued Debt Securities
		(Agency and Treasury)		11.1		17.8		8.0		6.0
	Corporate Debt Securities			16.5		22.5		9.1		15.6
	Asset-Backed Debt Securities			25.9		11.6		7.9		4.7
	Municipal Bonds			16.1		16.1		15.4		15.4
	Other Fixed Income Securities			18.8		17.5		16.6		15.1
Total Level 2			$	88.4	$	85.5	$	57.0	$	56.8
Total Marketable Securities			$	131.3	$	129.5	$	57.1	$	57.1