Revenue From Contracts With Customers (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Allowance for doubtful accounts	$ 19		$ 17
Market Services | Services transferred at a point in time
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue recognized (percentage)	70.50%	73.20%
Market Services | Services transferred over time
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue recognized (percentage)	29.50%	26.80%