Summary of Significant Accounting Principles and Practices Schedule Of Change In Presentation (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Operating income (loss)	$ 499	$ 262	$ (16)	$ 799	$ 601	$ 256	$ (127)	$ 335	$ 1,544	$ 1,065	$ 1,811
Other income (expense)										(125)	(137)
As Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Operating income (loss)										979	1,638
Other income (expense)										(39)	36
Adjustments | Accounting Standards Update 2017-07
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Operating income (loss)										86	173
Other income (expense)										$ (86)	$ (173)