Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended				12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Jun. 30, 2018	Sep. 30, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Federal statutory tax rate					21.00%	21.00%	35.00%
Tax Cuts and Jobs Act of 2017, deferred tax liability, income tax expense (benefit) total							$ (5,935)
Tax Cuts And Jobs Act of 2017, operating expense (benefit) from equity-method affiliates adjustments							(212)
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability		$ (21)	$ (31)	$ 33
Total accrued liabilities for interest and penalties					$ 3	$ 8
Total interest and penalties recognized as part of income tax expense	$ 11				$ (4)	$ (1)	$ (3)
Tax expense recognized as a part of income tax examination	10
Interest expense recognized as a part of income tax examination	$ 1
Income tax examination refund			$ 19	62
Income tax examination tax refund from settlement with taxing authority				60
Income tax examination interest refund from settlement with taxing authority				$ 2
Internal Revenue Service (IRS) [Member]
Federal statutory tax rate							35.00%
Tax Cuts and Jobs Act 2017 [Member]
Tax Cuts and Jobs Act of 2017, bonus depreciation on certain capital expenditures percentage						100.00%
Tax Cuts and Jobs Act 2017 [Member] | Internal Revenue Service (IRS) [Member]
Federal statutory tax rate						21.00%