Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended	12 Months Ended
	Dec. 31, 2019	Jun. 30, 2019	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax [Line Items]
Income tax expense (benefit)					$ (547)	$ (30)	$ 230
Current income tax expense (benefit)					(219)	(5)	(17)
Deferred income tax expense (benefit)					$ (328)	(25)	247
Valuation allowance against deferred tax assets, percent				100.00%	100.00%
Unrecognized tax benefits increased						14
Gain on sale of aggregate ownership interests, before-tax					$ (1)	222	2,593
Deferred tax benefit resulting from release of valuation allowance position; allocated to discontinued operations							$ 259
Net operating loss carryforwards, deferred tax assets	$ 306				238	306
Deferred Tax Assets, Net					16
Capital loss carryforwards					547
Deferred Tax Assets, Valuation Allowance	106				1,355	106
Investment in subsidiary					441
Unrecognized tax benefits, interest expense (benefit) and penalties					0	(5)
Unrecognized tax benefits, interest and penalties	0				0	0
Unrecognized tax benefit that would impact effective tax rate	65				23	65
Unrecognized tax benefits, decrease resulting from prior period tax positions					42
Deferred unrecognized tax benefits	7				50	$ 7
United States Federal [Member]
Income Tax [Line Items]
Net operating loss carryforwards					581
United States Federal [Member] | Expiring in 2037 [Member]
Income Tax [Line Items]
Net operating loss carryforwards					431
Various U.S. States [Member]
Income Tax [Line Items]
Net operating loss carryforwards					2,500
Canada [Member]
Income Tax [Line Items]
Deferred Tax Assets, Net					16
Capital loss carryforwards					593
Deferred Tax Assets, Valuation Allowance					577
Investment in subsidiary					$ 441
Minimum [Member] | United States Federal [Member]
Income Tax [Line Items]
Net operating loss carryforward, expiration date					Dec. 31, 2037
Minimum [Member] | Various U.S. States [Member]
Income Tax [Line Items]
Net operating loss carryforward, expiration date					Dec. 31, 2021
Maximum [Member] | Various U.S. States [Member]
Income Tax [Line Items]
Net operating loss carryforward, expiration date					Dec. 31, 2040
EnLink and General Partner [Member]
Income Tax [Line Items]
Effective close date of divestiture							Jul. 18, 2018
Gain on sale of aggregate ownership interests, before-tax			$ 2,600				$ 2,600
U.S. [Member]
Income Tax [Line Items]
Income tax expense (benefit)	$ (16)
Canadian Business Segment [Member]
Income Tax [Line Items]
Effective close date of divestiture						Jun. 27, 2019
Gain on sale of aggregate ownership interests, before-tax		$ 223
CARES Act [Member]
Income Tax [Line Items]
Income tax expense (benefit)					$ (113)
Current income tax expense (benefit)					(220)
Deferred income tax expense (benefit)					$ 107