Segment and Related Information (Geographic Data) (Details) - USD ($) $ in Millions		3 Months Ended																12 Months Ended
		Dec. 31, 2016		Sep. 30, 2016	[1]	Jun. 30, 2016	[1]	Mar. 31, 2016	[1]	Dec. 31, 2015		Sep. 30, 2015	[1]	Jun. 30, 2015	[1]	Mar. 31, 2015	[1]	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues from external customers		$ 1,832	[1]	$ 1,889		$ 1,785		$ 2,011		$ 1,780	[1]	$ 1,878		$ 1,781		$ 2,230		$ 7,517	$ 7,669	$ 7,852
Long-lived assets		30,772								31,056								30,772	31,056
U.S. [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues from external customers																		5,310	5,259	5,231
Long-lived assets		19,595								18,569								19,595	18,569
U.K. [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	[2]	11,177								12,487								11,177	12,487
U.K. Regulated [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues from external customers	[3]																	2,207	2,410	$ 2,621
Segment Reporting, Disclosure of Entity's Reportable Segments [Abstract]
Net property, plant and equipment not subject to accounting for the effects of certain types of regulation		$ 10,800								$ 12,200								$ 10,800	$ 12,200

[1] Quarterly results can vary depending on, among other things, weather. Accordingly, comparisons among quarters of a year may not be indicative of overall trends and changes in operations.

[2] Includes $10.8 billion and $12.2 billion of net PP&E as of December 31, 2016 and December 31, 2015. WPD is not subject to accounting for the effects of certain types of regulation as prescribed by GAAP.

[3] See Note 1 for additional information on Operating Revenues.