Goodwill (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2014
Changes in the Carrying Amount of Goodwill by Segment [Roll Forward]
Balance at beginning of period	$ 4,225	[1]
Allocation to discontinued operations	(82)	[2]
Effect of foreign currency exchange rates	44
Balance at end of period	4,187	[1]
United Kingdom Regulated [Member]
Changes in the Carrying Amount of Goodwill by Segment [Roll Forward]
Balance at beginning of period	3,143	[1]
Allocation to discontinued operations	0
Effect of foreign currency exchange rates	44
Balance at end of period	3,187	[1]
Kentucky Regulated [Member]
Changes in the Carrying Amount of Goodwill by Segment [Roll Forward]
Balance at beginning of period	662	[1]
Allocation to discontinued operations	0
Effect of foreign currency exchange rates	0
Balance at end of period	662	[1]
Supply [Member]
Changes in the Carrying Amount of Goodwill by Segment [Roll Forward]
Balance at beginning of period	420	[1]
Allocation to discontinued operations	(82)	[2]
Effect of foreign currency exchange rates	0
Balance at end of period	$ 338	[1]

[1] There were no accumulated impairment losses related to goodwill.

[2] Represents goodwill allocated to the Montana hydroelectric generating facilities which met the held for sale criteria at September 30, 2014. See Note 8 for additional information.