Segment and Related Information - Financial Data for Products and Services (Details) - USD ($) $ in Millions |
3 Months Ended | |
|---|---|---|
Mar. 31, 2017 |
Mar. 31, 2016 |
|
| Revenue from External Customer [Line Items] | ||
| Electric Utilities' Revenues | $ 4,131 | $ 3,981 |
| Gas Revenue | 1,560 | |
| Retail [Member] | ||
| Revenue from External Customer [Line Items] | ||
| Electric Utilities' Revenues | 3,394 | 3,377 |
| Wholesale [Member] | ||
| Revenue from External Customer [Line Items] | ||
| Electric Utilities' Revenues | 531 | 396 |
| Other [Member] | ||
| Revenue from External Customer [Line Items] | ||
| Electric Utilities' Revenues | 206 | $ 208 |
| Gas Distribution Operations [Member] | ||
| Revenue from External Customer [Line Items] | ||
| Gas Revenue | 1,132 | |
| Gas Marketing Services [Member] | ||
| Revenue from External Customer [Line Items] | ||
| Gas Revenue | 288 | |
| Other Gas Revenue [Member] | ||
| Revenue from External Customer [Line Items] | ||
| Gas Revenue | $ 140 | |