Restructuring Charges (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Restructuring Cost and Reserve [Line Items]
Severance, asset impairment and other restructuring charges	$ 31	$ 51	$ 106	$ 128
2016 Plan
Restructuring Cost and Reserve [Line Items]
Severance, asset impairment and other restructuring charges	31	51	106	128
2016 Plan | Other Restructuring
Restructuring Cost and Reserve [Line Items]
Other restructuring costs	9	15	50	20
Asset impairment charges			12
2016 Plan | Employee Severance
Restructuring Cost and Reserve [Line Items]
Severance costs	22	36	56	$ 108
2016 Plan | Other Restructuring Less Asset Write-Offs [Member]
Restructuring Cost and Reserve [Line Items]
Other restructuring costs	$ 9		$ 38
2015 Plan | Other Restructuring
Restructuring Cost and Reserve [Line Items]
Other restructuring costs		$ 15