Asset Impairment Expense (Tables)

9 Months Ended

Sep. 30, 2016

Impairment or Disposal of Tangible Assets Disclosure [Abstract]

Details of Impairment of Long-Lived Assets Held and Used by Asset

	Three Months Ended September 30,				Nine Months Ended September 30,
(in millions)	2016		2015		2016		2015
Buffalo Gap I	$	78	$	—	$	78	$	—
Buffalo Gap II	—		—		159		—
DPL	—		—		235		—
Kilroot	—		113		—		113
UK Wind	—		—		—		37
Buffalo Gap III	—		118		—		118
Other	1		—		1		8
Total asset impairment expense	$	79	$	231	$	473	$	276