Selected Balance Sheet Data - Accounts Receivable (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Accounts Receivable, Net
Accounts receivable	$ 68	$ 78
Less allowance for bad debts	(7)	(8)
Accounts receivable, net	$ 61	$ 70

Amount, after allowance for credit loss, of right to consideration from customer for product sold and service rendered in normal course of business, classified as current.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Name:	us-gaap_AccountsReceivableNetCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant