Restructuring and Other Charges - Activity and Reserve Balances for Restructuring Charges (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance			$ 58	$ 59	$ 59
Cash payments			(30)		(65)
Restructuring charges			28		65
Other			(23)		(1)
Restructuring reserve ending balance	$ 33		33		58
Restructuring and other charges	15	$ 26	22	99
Layoff costs
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance			56	50	50
Cash payments			(30)		(59)
Restructuring charges			23		64
Other			(23)		1
Restructuring reserve ending balance	26		26		56
Other exit costs
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance			2	$ 9	9
Cash payments			0		(6)
Restructuring charges			5		1
Other			0		(2)
Restructuring reserve ending balance	$ 7		7		2
Pension costs
Restructuring Reserve [Roll Forward]
Restructuring and other charges			$ 14
Stock awards reversal
Restructuring Reserve [Roll Forward]
Restructuring and other charges					$ 13