Commitments and Contingencies - Schedule of Long-term Commitments (Detail) $ in Millions | Jun. 30, 2019USD ($) |
Commitments And Contingencies Disclosure [Abstract] | |
Future Minimum Purchased Power Payments Due, 2019 | $ 23 |
Future Minimum Purchased Power Payments Due, 2020 | 0 |
Future Minimum Purchased Power Payments Due, 2021 | 0 |
Future Minimum Purchased Power Payments Due, 2022 | 0 |
Future Minimum Purchased Power Payments Due, 2023 | 0 |
Future Minimum Purchased Power Payments Due, Thereafter | 0 |
Total future minimum purchased power payments due | 23 |
Future Minimum Transportation Payments Due, 2019 | 100 |
Future Minimum Transportation Payments Due, 2020 | 196 |
Future Minimum Transportation Payments Due, 2021 | 191 |
Future Minimum Transportation Payments Due, 2022 | 184 |
Future Minimum Transportation Payments Due, 2023 | 161 |
Future Minimum Transportation Payments Due, Thereafter | 1,647 |
Total future minimum transportation payments due | 2,479 |
Future Minimum Capital Projects Payments Due, 2019 | 246 |
Future Minimum Capital Projects Payments Due, 2020 | 86 |
Future Minimum Capital Projects Payments Due, 2021 | 35 |
Future Minimum Capital Projects Payments Due, 2022 | 9 |
Future Minimum Capital Projects Payments Due, 2023 | 3 |
Future Minimum Capital Projects Payments Due, Thereafter | 13 |
Total future minimum capital projects payments due | 392 |
Future Minimum Fuel and Gas Supply Payments Due, 2019 | 125 |
Future Minimum Fuel and Gas Supply Payments Due, 2020 | 33 |
Future Minimum Fuel and Gas Supply Payments Due, 2021 | 3 |
Future Minimum Fuel and Gas Supply Payments Due, 2022 | 3 |
Future Minimum Fuel and Gas Supply Payments Due, 2023 | 1 |
Future Minimum Fuel and Gas Supply Payments Due, Thereafter | 0 |
Total future minimum fuel and gas supply payments due | 165 |
Future Minimum Long-term Service Agreements Payments Due, 2019 | 3 |
Future Minimum Long-term Service Agreements Payments Due, 2020 | 6 |
Future Minimum Long-term Service Agreements Payments Due, 2021 | 7 |
Future Minimum Long-term Service Agreements Payments Due, 2022 | 7 |
Future Minimum Long-term Service Agreements Payments Due, 2023 | 11 |
Future Minimum Long-term Service Agreements Payments Due, Thereafter | 78 |
Total future minimum long-term service agreements payments due | 112 |
Future Minimum Operating Leases Payments Due, 2019 | 1 |
Future Minimum Operating Leases Payments Due, 2020 | 2 |
Future Minimum Operating Leases Payments Due, 2021 | 2 |
Future Minimum Operating Leases Payments Due, 2022 | 2 |
Future Minimum Operating Leases Payments Due, 2023 | 2 |
Future Minimum Operating Leases Payments Due, Thereafter | 35 |
Total future minimum operating leases payments due | 44 |
Future Minimum Demand Side Management Payments Due, 2019 | 2 |
Future Minimum Demand Side Management Payments Due, 2020 | 1 |
Future Minimum Demand Side Management Payments Due, 2021 | 0 |
Future Minimum Demand Side Management Payments Due, 2022 | 0 |
Future Minimum Demand Side Management Payments Due, 2023 | 0 |
Future Minimum Demand Side Management Payments Due, Thereafter | 0 |
Total future minimum demand side management payments due | 3 |
Future Minimum Payments Due, 2019 | 500 |
Future Minimum Payments Due, 2020 | 324 |
Future Minimum Payments Due, 2021 | 238 |
Future Minimum Payments Due, 2022 | 205 |
Future Minimum Payments Due, 2023 | 178 |
Future Minimum Payments Due, Thereafter | 1,773 |
Total future minimum payments | $ 3,218 |