Accounts Receivable (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018
Accounts receivable
Other				$ 1,000,000	$ 4,000,000
Total accounts receivable, gross, current				553,000,000	587,000,000
Less: allowance for doubtful accounts	$ (39,000,000)	$ (47,000,000)	$ (47,000,000)	(39,000,000)	(41,000,000)
Accounts receivable, less allowance				514,000,000	546,000,000
Customer receivable in excess of 10% of accounts receivable				0
Changes in allowance for doubtful accounts
Beginning balance	41,000,000	47,000,000	53,000,000
Additions	51,000,000	60,000,000	74,000,000
Deductions	(53,000,000)	(66,000,000)	(80,000,000)
Ending balance	$ 39,000,000	$ 41,000,000	$ 47,000,000
Earned and unbilled receivables
Accounts receivable
Total accounts receivable, gross, current				81,000,000	92,000,000
Trade and purchased receivables
Accounts receivable
Total accounts receivable, gross, current				$ 471,000,000	$ 491,000,000