Revenue Recognition Accounting Policy (Details 3) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jan. 01, 2018
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total Revenues	$ 1,368	$ 1,448	$ 2,739	$ 2,865
Deferred Revenue	$ 394		394		$ 392
Deferred Revenue, Revenue Recognized			(31)
Deferred Revenue, Additions			40
Foreign Currency Gain (Loss) [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Deferred Revenue, Period Increase (Decrease)			$ (7)