SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Valuation and Qualifying Accounts Disclosure [Line Items]
Valuation Allowances and Reserves, Beginning Balance	$ 165,549,000	$ 115,689,000	$ 119,190,000
Valuation Allowances and Reserves, Charged to Cost and Expense	55,465,000	36,275,000	16,420,000
Valuation Allowances and Reserves, Charged to Other Accounts	37,744,000	34,761,000	40,663,000
Valuation Allowances and Reserves, Deductions	87,507,000	80,462,000	60,584,000
Valuation Allowances and Reserves, Ending Balance	171,251,000	165,549,000	115,689,000
Uncollectible Hardship Accounts Receivable Reserves		68,600,000
Impact Related To Nstar Merger	0	59,286,000
The Connecticut Light And Power Company [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Valuation Allowances and Reserves, Beginning Balance	77,571,000	83,475,000	82,173,000
Valuation Allowances and Reserves, Charged to Cost and Expense	3,947,000	2,080,000	3,215,000
Valuation Allowances and Reserves, Charged to Other Accounts	27,258,000	27,084,000	33,911,000
Valuation Allowances and Reserves, Deductions	26,781,000	35,068,000	35,824,000
Valuation Allowances and Reserves, Ending Balance	81,995,000	77,571,000	83,475,000
NSTAR Electric Company [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Valuation Allowances and Reserves, Beginning Balance	44,115,000	27,118,000	29,033,000
Valuation Allowances and Reserves, Charged to Cost and Expense	28,108,000	40,301,000	22,582,000
Valuation Allowances and Reserves, Charged to Other Accounts	0	0	0
Valuation Allowances and Reserves, Deductions	30,544,000	23,304,000	24,497,000
Valuation Allowances and Reserves, Ending Balance	41,679,000	44,115,000	27,118,000
Public Service Company Of New Hampshire [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Valuation Allowances and Reserves, Beginning Balance	6,760,000	7,190,000	6,824,000
Valuation Allowances and Reserves, Charged to Cost and Expense	6,608,000	6,457,000	7,035,000
Valuation Allowances and Reserves, Charged to Other Accounts	779,000	2,481,000	1,334,000
Valuation Allowances and Reserves, Deductions	6,783,000	9,368,000	8,003,000
Valuation Allowances and Reserves, Ending Balance	7,364,000	6,760,000	7,190,000
Western Massachusetts Electric Company [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Valuation Allowances and Reserves, Beginning Balance	8,501,000	10,018,000	12,891,000
Valuation Allowances and Reserves, Charged to Cost and Expense	2,580,000	2,294,000	3,133,000
Valuation Allowances and Reserves, Charged to Other Accounts	4,299,000	2,428,000	1,141,000
Valuation Allowances and Reserves, Deductions	5,396,000	6,239,000	7,147,000
Valuation Allowances and Reserves, Ending Balance	9,984,000	8,501,000	10,018,000
Uncollectible Hardship Accounts Receivable Reserves		5,400,000
Yankee Gas Services Company [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Uncollectible Hardship Accounts Receivable Reserves		$ 6,800,000