Employee Benefit Plans - BHE - Employer Contributions (Details) - 9 months ended Sep. 30, 2021 £ in Millions, $ in Millions	USD ($)	GBP (£)	GBP (£)
Other Postretirement Plans
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, expected contributions in current fiscal year	$ 13
Employer contributions	10
United States | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, expected contributions in current fiscal year	13
Employer contributions	9
United Kingdom | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, expected contributions in current fiscal year | £			£ 20
Employer contributions	$ 24	£ 17