Goodwill and Other Intangible Assets (Goodwill) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Changes in the Carrying Amount of Goodwill by Segment [Roll Forward]
Balance at beginning of period	$ 3,198	$ 3,162
Effect of foreign currency exchange rates	76	34
Other	0	2
Balance at end of period	3,274	3,198
U.K. Regulated [Member]
Changes in the Carrying Amount of Goodwill by Segment [Roll Forward]
Balance at beginning of period	2,483	2,447
Effect of foreign currency exchange rates	76	34
Other	0	2
Balance at end of period	2,559	2,483
Kentucky Regulated [Member]
Changes in the Carrying Amount of Goodwill by Segment [Roll Forward]
Balance at beginning of period	662	662
Effect of foreign currency exchange rates	0	0
Other	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	53	53
Effect of foreign currency exchange rates	0	0
Other	0	0
Balance at end of period	$ 53	$ 53