CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Statement [Abstract]
Operating Revenues	$ 9,863,085	$ 8,904,430	$ 8,526,470
Operating Expenses:
Purchased Power and Transmission	3,372,344	2,987,840	3,040,160
Operations and Maintenance	1,739,685	1,480,252	1,363,113
Depreciation	1,103,008	981,380	885,278
Amortization of Regulatory Assets, Net	231,965	177,679	195,380
Energy Efficiency Programs	592,775	535,760	501,369
Taxes Other Than Income Taxes	829,987	752,785	711,035
Impairment of Northern Pass Transmission	0	0	239,644
Total Operating Expenses	7,869,764	6,915,696	6,935,979
Operating Income	1,993,321	1,988,734	1,590,491
Interest Expense	582,334	538,452	533,197
Other Income, Net	161,282	108,590	132,777
Income Before Income Tax Expense	1,572,269	1,558,872	1,190,071
Income Tax Expense	344,223	346,186	273,499
Net Income	1,228,046	1,212,686	916,572
Net Income Attributable to Noncontrolling Interests	7,519	7,519	7,519
Net Income Attributable to Common Shareholders	$ 1,220,527	$ 1,205,167	$ 909,053
Basic Earnings Per Common Share (in dollars per share)	$ 3.55	$ 3.56	$ 2.83
Diluted Earnings Per Common Share (in dollars per share)	$ 3.54	$ 3.55	$ 2.81
Weighted Average Common Shares Outstanding:
Basic (in shares)	343,972,926	338,836,147	321,416,086
Diluted (in shares)	344,631,056	339,847,062	322,941,636