Goodwill and Other Intangible Assets (Goodwill) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Changes in the Carrying Amount of Goodwill by Segment [Roll Forward]
Balance at beginning of period	$ 3,258	$ 3,060
Effect of foreign currency exchange rates	(149)	198
Goodwill recognized during the period	53	0
Balance at end of period	3,162	3,258
U.K. Regulated [Member]
Changes in the Carrying Amount of Goodwill by Segment [Roll Forward]
Balance at beginning of period	2,596	2,398
Effect of foreign currency exchange rates	(149)	198
Goodwill recognized during the period	0	0
Balance at end of period	2,447	2,596
Kentucky Regulated [Member]
Changes in the Carrying Amount of Goodwill by Segment [Roll Forward]
Balance at beginning of period	662	662
Goodwill recognized during the period	0	0
Balance at end of period	662	662
Corporate And Other [Member]
Changes in the Carrying Amount of Goodwill by Segment [Roll Forward]
Balance at beginning of period	0	0
Goodwill recognized during the period	53	0
Balance at end of period	$ 53	$ 0