Revenues Revenues Recognized from Performance Obligations Satisfied in Prior Periods (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Contract with Customer, Performance Obligation Satisfied in Previous Period [Line Items]
Contract with Customer, Performance Obligation Satisfied in Previous Period	$ 171	$ 131	$ 326	$ 228
Change in estimate variable consideration [Member]
Contract with Customer, Performance Obligation Satisfied in Previous Period [Line Items]
Contract with Customer, Performance Obligation Satisfied in Previous Period	$ 193	$ 91	$ 300	$ 4