Asset Impairment Expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Asset Impairment Expense [Line Items]
Impairment of Long-Lived Assets Held-for-use	$ 116	$ 92	$ 116	$ 92
Kilroot and Ballylumford [Member]
Asset Impairment Expense [Line Items]
Impairment of Long-Lived Assets Held-for-use	115	0	115	0
Assets Carrying Amount Disclosure Nonrecurring	114		114
Shady Point [Member]
Asset Impairment Expense [Line Items]
Impairment of Long-Lived Assets Held-for-use	0	83	0	83
Assets Carrying Amount Disclosure Nonrecurring		127		127
Other Subsidiaries [Member]
Asset Impairment Expense [Line Items]
Impairment of Long-Lived Assets Held-for-use	$ 1	$ 9	$ 1	$ 9