Restructuring Charges (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Restructuring Cost and Reserve [Line Items]
Severance, asset impairment and other restructuring charges	$ 34	$ 22	$ 140	$ 150
Asset Impairment Charges		436	0	436
2016 Plan
Restructuring Cost and Reserve [Line Items]
Severance, asset impairment and other restructuring charges	34	22	140	150
2016 Plan | Other Restructuring
Restructuring Cost and Reserve [Line Items]
Other restructuring costs	19	4	69	24
Asset Impairment Charges			12
2016 Plan | Employee Severance
Restructuring Cost and Reserve [Line Items]
Severance costs	15	18	71	$ 126
2016 Plan | Other Restructuring Less Asset Write-Offs [Member]
Restructuring Cost and Reserve [Line Items]
Other restructuring costs	$ 19		$ 57
2015 Plan | Other Restructuring
Restructuring Cost and Reserve [Line Items]
Other restructuring costs		$ 4