Revenues - Receivables (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Revenue from Contract with Customer [Abstract]
Receivables for Product and Services in Accounts Receivable, Net	$ 792	$ 1,156
Accounts Receivable, after Allowance for Credit Loss, Current	792	1,156
Equipment Receivables	34	85
Contract with Customer, Asset, after Allowance for Credit Loss	7	3
Contract with Customer, Liability	$ 37	$ 12