Asset Impairment Expense (Narrative) (Details) - USD ($) $ in Millions		3 Months Ended			12 Months Ended
		Sep. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Apr. 12, 2019
Asset Impairment Expense [Line Items]
Impairment of Long-Lived Assets Held-for-use					$ 864	$ 185	$ 208
Other Asset Impairment Charges		$ 849	$ 69	$ 116	864	185	208
Long-Lived Assets			22,822		23,103	22,822
Hawaii Subsidiary [Member]
Asset Impairment Expense [Line Items]
Impairment of Long-Lived Assets Held-for-use		$ 38			38	60	0
Kilroot and Ballylumford [Member]
Asset Impairment Expense [Line Items]
Impairment of Long-Lived Assets Held-for-use					0	115	0
Assets carrying amount			$ 114			114
Shady Point [Member]
Asset Impairment Expense [Line Items]
Impairment of Long-Lived Assets Held-for-use					0	0	157
Assets carrying amount							30
Nejapa [Member]
Asset Impairment Expense [Line Items]
Impairment of Long-Lived Assets Held-for-use					0	0	37
Assets carrying amount							$ 5
Long Lived Assets Held And Used [Member] | Hawaii Subsidiary [Member]
Asset Impairment Expense [Line Items]
Impairment of Long-Lived Assets Held-for-use					60
Assets carrying amount					$ 103
Long Lived Assets Held And Used [Member] | Kilroot and Ballylumford [Member]
Asset Impairment Expense [Line Items]
Other Asset Impairment Charges	[1]					115
Assets carrying amount								$ 232
Long Lived Assets Held And Used [Member] | Nejapa [Member]
Asset Impairment Expense [Line Items]
Other Asset Impairment Charges	[2]					$ 60

[1] Per the Company's policy, pre-tax loss is limited to the impairment of long-lived assets. Any additional loss will be recognized on completion of the sale. See Note 22—Asset Impairment Expense and Note 25—Held-for-Sale and Dispositions for further information.

[2] See Note 22—Asset Impairment Expense for further information.(3)See Note 8—Investments In and Advances to Affiliates for further information.