Segment and Related Information (Geographic Data) (Details) - USD ($) $ in Millions |
3 Months Ended | 12 Months Ended | |||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Dec. 31, 2019 |
Sep. 30, 2019 |
Jun. 30, 2019 |
Mar. 31, 2019 |
Dec. 31, 2018 |
Sep. 30, 2018 |
Jun. 30, 2018 |
Mar. 31, 2018 |
Dec. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
|
Revenues from External Customers and Long-Lived Assets [Line Items] | |||||||||||
Revenues from external customers | $ 1,954 | $ 1,933 | $ 1,803 | $ 2,079 | $ 1,939 | $ 1,872 | $ 1,848 | $ 2,126 | $ 7,769 | $ 7,785 | $ 7,447 |
Long-lived assets | 37,225 | 35,175 | 37,225 | 35,175 | |||||||
U.S. [Member] | |||||||||||
Revenues from External Customers and Long-Lived Assets [Line Items] | |||||||||||
Revenues from external customers | 5,602 | 5,517 | 5,356 | ||||||||
Long-lived assets | 23,607 | 22,384 | 23,607 | 22,384 | |||||||
U.K. [Member] | |||||||||||
Revenues from External Customers and Long-Lived Assets [Line Items] | |||||||||||
Long-lived assets | $ 13,618 | $ 12,791 | 13,618 | 12,791 | |||||||
U.K. Regulated [Member] | |||||||||||
Revenues from External Customers and Long-Lived Assets [Line Items] | |||||||||||
Revenues from external customers | $ 2,167 | $ 2,268 | $ 2,091 |