CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating Activities:
Net Income	$ 1,228,046	$ 1,212,686	$ 916,572
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Depreciation	1,103,008	981,380	885,278
Deferred Income Taxes	347,056	257,154	209,812
Uncollectible Expense	60,886	53,461	63,446
Pension, SERP and PBOP (Income)/Expense, Net	(14,693)	12,888	22,000
Pension and PBOP Contributions	(182,344)	(111,524)	(121,782)
Regulatory Underrecoveries, Net	(314,211)	(516,411)	(124,870)
Reserve at CL&P related to PURA Settlement Agreement and Storm Performance Penalty	81,274	0	0
Amortization	231,965	177,679	195,380
Payments Related to CYAPC's DOE Pre-1983 Spent Nuclear Fuel Obligation	0	0	(29,000)
Proceeds from DOE Spent Nuclear Fuel Litigation	0	0	68,840
Impairment of Northern Pass Transmission	0	0	239,644
Cost of Removal Expenditures	(242,130)	(148,332)	(153,477)
Other	(64,640)	(25,957)	(42,610)
Changes in Current Assets and Liabilities:
Accounts Receivables from Subsidiaries	(135,505)	(351,843)	(98,716)
Fuel, Materials, Supplies and REC Inventory	(1,859)	(15,404)	(8,074)
Taxes Receivable/Accrued, Net	(110,621)	43,819	(16,129)
Accounts Payable	(29,201)	122,567	14,866
Other Current Assets and Liabilities, Net	5,569	(9,591)	(11,603)
Net Cash Flows Provided by Operating Activities	1,962,600	1,682,572	2,009,577
Investing Activities:
Investments in Property, Plant and Equipment	(3,175,080)	(2,942,996)	(2,911,489)
Proceeds from Sales of Marketable Securities	447,893	434,124	566,592
Purchases of Marketable Securities	(414,980)	(401,823)	(537,258)
Acquisition of Assets of Columbia Gas of Massachusetts, Net of Restricted Cash	0	(1,113,252)	0
Investments in Unconsolidated Affiliates, Net	(327,385)	(239,673)	(416,337)
Other Investing Activities	22,178	23,809	24,204
Net Cash Flows Used in Investing Activities	(3,447,374)	(4,129,275)	(3,274,288)
Financing Activities:
Issuance of Common Shares, Net of Issuance Costs	0	928,992	852,254
Cash Dividends on Common Shares	(805,439)	(744,665)	(663,239)
Cash Dividends on Preferred Stock	(7,519)	(7,519)	(7,519)
(Decrease)/Increase in Notes Payable	256,125	13,955	325,370
Repayment of Rate Reduction Bonds	(43,210)	(43,210)	(52,332)
Issuance of Long-Term Debt	3,230,000	2,760,000	1,520,000
Retirement of Long-Term Debt	(1,142,500)	(327,236)	(801,078)
Other Financing Activities	(46,625)	14,273	(1,006)
Net Cash Flows Provided by Financing Activities	1,440,832	2,594,590	1,172,450
Net (Decrease)/Increase in Cash and Restricted Cash	(43,942)	147,887	(92,261)
Cash and Restricted Cash - Beginning of Year	264,950	117,063	209,324
Cash and Restricted Cash - End of Year	221,008	264,950	117,063
Hingham Water System
Investing Activities:
Proceeds from the Sale of Generation Assets	$ 0	$ 110,536	$ 0