SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT - BALANCE SHEET (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current Assets:
Cash	$ 108,068	$ 38,165
Prepayments and Other Current Assets	260,995	138,009
Total Current Assets	2,292,224	2,487,099
Deferred Debits and Other Assets:
Investments in Subsidiary Companies, at Equity	463,700	277,600
Goodwill	4,427,266	4,427,266
Other Long-Term Assets	862,693	605,692
Total Deferred Debits and Other Assets	10,338,604	10,115,824
Total Assets	38,241,256	36,220,386
Current Liabilities:
Notes Payable	910,000	1,088,087
Long-Term Debt – Current Portion	837,319	549,631
Accounts Payable	1,119,995	1,085,034
Other Current Liabilities	823,006	738,222
Total Current Liabilities	4,112,882	3,589,045
Total Deferred Credits and Other Liabilities	9,653,913	9,613,640
Capitalization:
Long-Term Debt	12,248,743	11,775,889
Common Shareholders' Equity:
Common Shares	1,669,392	1,669,392
Capital Surplus, Paid in	6,241,222	6,239,940
Retained Earnings	3,953,974	3,561,084
Accumulated Other Comprehensive Loss	(60,000)	(66,403)
Treasury Stock	(317,771)	(317,771)
Common Shareholders' Equity	11,486,817	11,086,242	$ 10,711,734	$ 10,352,215
Total Liabilities and Capitalization	38,241,256	36,220,386
Eversource
Current Assets:
Cash	591	521	$ 93	$ 67
Accounts Receivable from Subsidiaries	32,175	3,397
Dividend Receivable from Subsidiary	0	150,000
Notes Receivable from Subsidiaries	991,400	844,500
Prepayments and Other Current Assets	26,861	18,568
Total Current Assets	1,051,027	1,016,986
Deferred Debits and Other Assets:
Investments in Subsidiary Companies, at Equity	12,009,659	10,945,986
Notes Receivable from Subsidiaries	323,500	312,190
Accumulated Deferred Income Taxes	40,454	47,940
Goodwill	3,231,811	3,231,811
Other Long-Term Assets	73,669	58,313
Total Deferred Debits and Other Assets	15,679,093	14,596,240
Total Assets	16,730,120	15,613,226
Current Liabilities:
Notes Payable	631,500	778,087
Long-Term Debt – Current Portion	378,883	32,114
Accounts Payable	286	292
Accounts Payable to Subsidiaries	8,432	18,242
Other Current Liabilities	57,591	56,601
Total Current Liabilities	1,076,692	885,336
Total Deferred Credits and Other Liabilities	134,614	118,176
Capitalization:
Long-Term Debt	4,031,997	3,523,472
Common Shareholders' Equity:
Common Shares	1,669,392	1,669,392
Capital Surplus, Paid in	6,241,222	6,239,940
Retained Earnings	3,953,974	3,561,084
Accumulated Other Comprehensive Loss	(60,000)	(66,403)
Treasury Stock	317,771	(317,771)
Common Shareholders' Equity	11,486,817	11,086,242
Total Liabilities and Capitalization	$ 16,730,120	$ 15,613,226