Supplemental Financial Information (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Variable Interest Entities
Assets	$ 52,663				$ 49,585				$ 52,663	$ 49,585
Revenues	6,874	$ 5,837	$ 6,075	$ 6,499	6,656	$ 6,481	$ 6,925	$ 6,936	25,285	26,998	$ 26,425
Operating income (loss)	1,083	$ 903	$ 1,251	$ 902	(44)	$ 984	$ 1,414	$ 1,792	4,139	4,146	$ 5,062
Lease Income
Lease income									133	148
ConsolidatedVIE [Member]
Variable Interest Entities
Ownership of consolidated VIE			51.00%
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entities
Assets	1,390				141				1,390	141
Liabilities	$ 197				$ 22				197	$ 22
Revenues									705
Operating income (loss)									$ 498