Other Expenses (Restructuring Charges) (Details) - Other expenses - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Lease and Asset Impairment
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 43	$ 12
Unit Cost Initiative | Severance
Restructuring Cost and Reserve [Line Items]
Balance at January 1,	23	22	$ 35
Restructuring charges	108	63	38
Cash payments	(74)	(62)	(51)
Balance at December 31,	57	23	22
Total restructuring charges incurred since inception of initiative	$ 244	$ 136	$ 73