Revenues - Contract Assets and Liabilities (Details) $ in Millions	6 Months Ended
Jun. 30, 2019 USD ($)
Contract Assets
Balance at December 31, 2018	$ 4
Increase due to revenue recognized during the period but contingent on future performance	12
Transferred to receivables from contract assets recognized at the beginning of the period	(11)
Balance at June 30, 2019	5
Contract Liabilities
Balance at December 31, 2018	64
Revenue recognized that was included in the deferred revenue balance at the beginning of the period	(44)
Increase due to cash received, excluding amount recognized as revenue during the period	29
Contract with Customer, Liability, Cumulative Catch-up Adjustment to Revenue, Modification of Contract	7
Balance at June 30, 2019	$ 56

Amount of increase (decrease) in revenue recognized for cumulative catch-up adjustment from change in measure of progress which increases (decreases) 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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Amount, after allowance for credit loss, of right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time.

+ References

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-Publisher FASB
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Amount of decrease in right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time from transfer to receivable due to right to consideration becoming unconditional.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable.

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Amount of increase (decrease) in obligation to transfer good or service to customer for which consideration from customer has been received or is due, from business combination.

+ References

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Amount of revenue recognized that was previously included in balance of obligation to transfer good or service to customer for which consideration from customer has been received or is due.

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