Financial Instruments - Fair Value Hedges (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Gain/(loss) recognized in income on fair value of hedges	$ 0	$ 0	$ 0	$ 0
Borrowings
Derivative Instruments, Gain (Loss) [Line Items]
Gain/(loss) recognized in income on fair value of hedges	0	2	1	4
Derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain/(loss) recognized in income on fair value of hedges	$ 0	$ (2)	$ (1)	$ (4)