Subsidiary Debt - Northern Powergrid (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Par value	$ 49,746
Subsidiary debt
Debt Instrument [Line Items]
Par value	36,545
Subsidiary debt	36,659	$ 36,319
Northern Powergrid \| Subsidiary debt
Debt Instrument [Line Items]
Par value	3,321
Subsidiary debt	$ 3,287	3,259
Northern Powergrid \| Subsidiary debt \| 4.133% European Investment Bank loans, due 2022
Debt Instrument [Line Items]
Stated rate	4.133%
Par value	$ 204
Subsidiary debt	$ 204	206
Northern Powergrid \| Subsidiary debt \| 7.25% Bonds, due 2022
Debt Instrument [Line Items]
Stated rate	7.25%
Par value	$ 271
Subsidiary debt	$ 269	277
Northern Powergrid \| Subsidiary debt \| 2.50% Bonds, due 2025
Debt Instrument [Line Items]
Stated rate	2.50%
Par value	$ 203
Subsidiary debt	$ 202	203
Northern Powergrid \| Subsidiary debt \| 2.073% European Investment Bank loan, due 2025
Debt Instrument [Line Items]
Stated rate	2.073%
Par value	$ 67
Subsidiary debt	$ 69	70
Northern Powergrid \| Subsidiary debt \| 2.564% European Investment Bank loans, due 2027
Debt Instrument [Line Items]
Stated rate	2.564%
Par value	$ 338
Subsidiary debt	$ 337	340
Northern Powergrid \| Subsidiary debt \| 7.25% Bonds, due 2028
Debt Instrument [Line Items]
Stated rate	7.25%
Par value	$ 251
Subsidiary debt	$ 254	257
Northern Powergrid \| Subsidiary debt \| 4.375% Bonds, due 2032
Debt Instrument [Line Items]
Stated rate	4.375%
Par value	$ 203
Subsidiary debt	$ 200	202
Northern Powergrid \| Subsidiary debt \| 5.125% Bonds, due 2035
Debt Instrument [Line Items]
Stated rate	5.125%
Par value	$ 271
Subsidiary debt	$ 268	270
Northern Powergrid \| Subsidiary debt \| 5.125% Bonds, due 2035
Debt Instrument [Line Items]
Stated rate	5.125%
Par value	$ 203
Subsidiary debt	$ 201	203
Northern Powergrid \| Subsidiary debt \| 2.750% Bonds, due 2049
Debt Instrument [Line Items]
Stated rate	2.75%
Par value	$ 203
Subsidiary debt	$ 200	202
Northern Powergrid \| Subsidiary debt \| 2.250% Bonds, due 2059
Debt Instrument [Line Items]
Stated rate	2.25%
Par value	$ 406
Subsidiary debt	$ 398	402
Northern Powergrid \| Subsidiary debt \| 1.875% Bonds, due 2062
Debt Instrument [Line Items]
Stated rate	1.875%
Par value	$ 406
Subsidiary debt	398	403
Northern Powergrid \| Subsidiary debt \| Variable-rate loan, due 2026
Debt Instrument [Line Items]
Par value	0
Subsidiary debt	0	$ 183
Interest rate on derivatives		89.00%
Variable rate		2.03%
Basis spread on variable rate		2.00%
Fixed interest rate		3.07%
Effective interest rate		2.96%
Northern Powergrid \| Subsidiary debt \| Variable-rate loan, due 2026
Debt Instrument [Line Items]
Par value	0
Subsidiary debt	0	$ 41
Variable rate		2.02%
Basis spread on variable rate		2.00%
Northern Powergrid \| Subsidiary debt \| Variable-rate loan, due 2026
Debt Instrument [Line Items]
Par value	295
Subsidiary debt	$ 287	$ 0
Interest rate on derivatives	80.00%
Variable rate	1.73%
Basis spread on variable rate	1.55%
Fixed interest rate	2.45%
Effective interest rate	2.30%

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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- Definition

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

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- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

The interest rate applicable to the portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a set, unchanging rate.

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Amount of long-term debt classified as other.

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- Definition

Percentage of an entity's outstanding debt that is designated as a hedged item in cash flow, fair value, or net investment hedge.

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