Derivative Instruments (Narrative) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2016	Sep. 30, 2019	Sep. 30, 2018	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Number of securities called by each warrant or right								84.5
Exercise price of warrants or rights								$ 6.43
Warrants and rights outstanding	$ 0			$ 0			$ 0
Fair Value Adjustment of Warrants	0	$ (11)		0	$ (67)
Foreign currency forward contracts
Derivative [Line Items]
Derivative, Notional Amount						$ 391	435
Other, Net | Not Designated as Hedging Instrument | Foreign currency forward contracts
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	(6)	$ (5)		(3)	$ (5)
Capital in Excess of Par Value
Derivative [Line Items]
Stock issued during period, shares, new issues			84.5
Other Current Liabilities [Member] | Not Designated as Hedging Instrument | Foreign currency forward contracts
Derivative [Line Items]
Derivative Liability, Fair Value, Gross Liability	$ 2			$ 2			$ 4