Revenue from contracts with customers transaction price allocated to remaining performance obligations (Detail 1) $ in Millions	Sep. 30, 2020 USD ($)
Electricity and Natural Gas [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Transaction price allocated to remaining performance obligations	$ 7,021
Other Sales and Service Contracts [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Transaction price allocated to remaining performance obligations	$ 3,663