Revenue Recognition (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue Recognition [Abstract]
Revenue, remaining performance obligation, amount	$ 86	$ 82	$ 82
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation, amount	86	$ 82	$ 82
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue Recognition [Abstract]
Revenue, remaining performance obligation, amount	64
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation, amount	$ 64
Revenue, remaining performance obligation, expected timing of satisfaction, period	1 year