Revenues from Contracts with Customers (Narrative) (Details) - USD ($)	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Deferred revenue	$ 260,000,000	$ 301,000,000
Expected period for satisfaction of performance obligation	three days
Receivables, Net Current, Including Assets Held For Sale	$ 144,000,000
Receivables	36,000,000	137,000,000
Allowance for doubtful accounts, receivables	0	$ 0
Disposal Group, Held-for-sale, Not Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal group, including discontinued operation, accounts, notes and loans receivable, net	$ 108,000,000