Revenues from Contracts with Customers (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2021	Dec. 31, 2020
Revenue from Contract with Customer [Abstract]
Deferred revenue	$ 339	$ 301
Expected period for satisfaction of performance obligation	three days
Receivables	$ 132	$ 137

The total amount due to the entity within one year of the balance sheet date (or one operating cycle, if longer) from outside sources, including trade accounts receivable, notes and loans receivable, as well as any other types of receivables, net of allowances established for the purpose of reducing such receivables to an amount that approximates their net realizable value.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant