Subsidiary Debt - EEGH - Maturities of Long-term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 1,839
Long-term Debt, Maturities, Repayments of Principal in Year Two	1,848
Long-term Debt, Maturities, Repayments of Principal in Year Three	3,200
Long-term Debt, Maturities, Repayments of Principal in Year Four	2,710
Long-term Debt, Maturities, Repayments of Principal in Year Five	2,525
Long-term Debt, Maturities, Repayments of Principal after Year Five	37,637
Par value	49,759
Long-term Debt	49,866	$ 39,353
Eastern Energy Gas Holdings, LLC [Member]
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	500
Long-term Debt, Maturities, Repayments of Principal in Year Two	0
Long-term Debt, Maturities, Repayments of Principal in Year Three	650
Long-term Debt, Maturities, Repayments of Principal in Year Four	1,050
Long-term Debt, Maturities, Repayments of Principal in Year Five	0
Long-term Debt, Maturities, Repayments of Principal after Year Five	2,255
Par value	4,455
Debt Instrument, Unamortized Premium, Discount and Debt Issuance Cost	(30)
Long-term Debt	$ 4,425	$ 5,520

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Face (par) amount of debt instrument at time of issuance.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount of long-term debt payable, sinking fund requirement, and other securities issued that are redeemable by holder at fixed or determinable price and date, maturing after fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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