Revenue from contracts with customers transaction price allocated to remaining performance obligations (Detail)
$ in Millions |
Dec. 31, 2018
USD ($)
|
| Electricity and Natural Gas [Member] |
|
| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] |
|
| Transaction price allocated to remaining performance obligations |
$ 6,520
|
| Electricity and Natural Gas [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01 |
|
| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] |
|
| Transaction price allocated to remaining performance obligations |
$ 842
|
| Performance obligations expected to be satisfied, period |
1 year
|
| Electricity and Natural Gas [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01 |
|
| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] |
|
| Transaction price allocated to remaining performance obligations |
$ 5,678
|
| Performance obligations expected to be satisfied, period |
|
| Other Sales and Service Contracts [Member] |
|
| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] |
|
| Transaction price allocated to remaining performance obligations |
$ 3,094
|
| Other Sales and Service Contracts [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01 |
|
| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] |
|
| Transaction price allocated to remaining performance obligations |
$ 1,190
|
| Performance obligations expected to be satisfied, period |
1 year
|
| Other Sales and Service Contracts [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01 |
|
| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] |
|
| Transaction price allocated to remaining performance obligations |
$ 1,904
|
| Performance obligations expected to be satisfied, period |
|