Revenues - Contract Assets and Liabilities (Details) $ in Millions	9 Months Ended
Sep. 30, 2018 USD ($)
Contract Assets
Balance at January 1, 2018	$ 10
Increase due to revenue recognized during the period but contingent on future performance	11
Transferred to receivables from contract assets recognized at the beginning of the period	(7)
Contract with Customer, Asset, Credit Loss Expense	(5)
Reclassified to asset held for sale	(2)
Balance at September 30, 2018	7
Contract Liabilities
Balance at January 1, 2018	42
Revenue recognized that was included in the deferred revenue balance at the beginning of the period	(74)
Increase due to cash received, excluding amount recognized as revenue during the period	75
Contract with Customer, Liability, Cumulative Catch-up Adjustment to Revenue, Modification of Contract	26
Reclassified to held for sale	(3)
Balance at September 30, 2018	$ 66

Amount of credit loss recognized for write-down of right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time.

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