SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT - BALANCE SHEET (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current Assets:
Cash	$ 106,599	$ 15,432
Prepayments and Other Current Assets	252,439	342,135
Total Current Assets	3,130,143	2,414,539
Deferred Debits and Other Assets:
Investments in Subsidiary Companies, at Equity	1,107,143	871,633
Goodwill	4,445,988	4,427,266
Other Long-Term Assets	583,854	512,238
Total Deferred Debits and Other Assets	12,086,932	11,123,906
Total Assets (as of)	46,099,598	41,123,915
Current Liabilities:
Notes Payable	1,249,325	889,084
Long-Term Debt – Current Portion	1,053,186	327,411
Other Current Liabilities	809,214	836,834
Total Current Liabilities	4,915,012	3,605,563
Deferred Credits and Other Liabilities	11,342,662	10,421,838
Capitalization:
Long-Term Debt	15,125,876	13,770,828
Common Shareholders' Equity:
Common Shares	1,789,092	1,729,292
Capital Surplus, Paid in	8,015,663	7,087,768
Retained Earnings	4,613,201	4,177,048
Accumulated Other Comprehensive Loss	(76,411)	(65,059)
Treasury Stock	(277,979)	(299,055)
Stockholders' equity	14,063,566	12,629,994	$ 11,486,817	$ 11,086,242
Total Liabilities and Capitalization	46,099,598	41,123,915
Eversource
Current Assets:
Cash	434	1,469	$ 591	$ 521
Accounts Receivable from Subsidiaries	39,645	25,070
Notes Receivable from Subsidiaries	996,300	1,376,000
Prepayments and Other Current Assets	19,043	33,546
Total Current Assets	1,055,422	1,436,085
Deferred Debits and Other Assets:
Investments in Subsidiary Companies, at Equity	15,483,263	13,162,337
Notes Receivable from Subsidiaries	1,110,400	157,000
Accumulated Deferred Income Taxes	33,469	27,578
Goodwill	3,231,811	3,231,811
Other Long-Term Assets	90,735	92,394
Total Deferred Debits and Other Assets	19,949,678	16,671,120
Total Assets (as of)	21,005,100	18,107,205
Current Liabilities:
Notes Payable	1,054,325	878,584
Long-Term Debt – Current Portion	473,933	23,933
Accounts Payable to Subsidiaries	18,424	4,333
Other Current Liabilities	103,477	62,385
Total Current Liabilities	1,650,159	969,235
Deferred Credits and Other Liabilities	163,053	149,637
Capitalization:
Long-Term Debt	5,128,322	4,358,339
Common Shareholders' Equity:
Common Shares	1,789,092	1,729,292
Capital Surplus, Paid in	8,015,663	7,087,768
Retained Earnings	4,613,201	4,177,048
Accumulated Other Comprehensive Loss	(76,411)	(65,059)
Treasury Stock	(277,979)	(299,055)
Stockholders' equity	14,063,566	12,629,994
Total Liabilities and Capitalization	$ 21,005,100	$ 18,107,205