Investments In and Advances To Affiliates - Summarized Financial Information (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
Schedule of Equity Method Investments [Line Items]
Revenue	$ 2,560	$ 2,545	$ 2,217	$ 2,338	$ 2,431	$ 2,625	$ 2,483	$ 2,650	$ 9,660	$ 10,189	$ 10,736
Operating margin	906	756	524	507	560	701	502	586	2,693	2,349	2,573
Net income	401	$ (481)	$ 3	$ 229	(120)	$ 298	$ 67	$ 233	152	478	1,565
Assets, Current	5,414				5,231				5,414	5,231
Liabilities, Current	5,362				5,096				5,362	5,096
Liabilities, Noncurrent	23,649				22,435				23,649	22,435
Stockholders' Equity Attributable to Parent	2,634				2,996				2,634	2,996
Undistributed Earnings Of Minority Owned Affiliates Included In Retained Earnings	120								120
Distributions Received From Minority Owned Affiliates									14	23	83
Basis Difference Between Carrying Amount And Investment	150								150
Minority Owned Affiliates
Schedule of Equity Method Investments [Line Items]
Revenue									1,880	1,122	962
Operating margin									213	124	135
Net income									(538)	(724)	14
Assets, Current	1,017				831				1,017	831
Assets, Noncurrent	6,230				7,220				6,230	7,220
Liabilities, Current	1,294				1,271				1,294	1,271
Liabilities, Noncurrent	3,671				3,966				3,671	3,966
Stockholders' Equity Attributable to Parent	2,282				2,814				2,282	2,814
Majority Owned Affiliates
Schedule of Equity Method Investments [Line Items]
Revenue									1	49	40
Operating margin									(3)	(5)	3
Net income									(4)	(7)	$ (3)
Assets, Current	159				166				159	166
Assets, Noncurrent	886				982				886	982
Liabilities, Current	121				141				121	141
Liabilities, Noncurrent	981				1,052				981	1,052
Stockholders' Equity Attributable to Parent	$ (57)				$ (45)				$ (57)	$ (45)