Revenue from Contracts with Customers - Contract Balances (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Contract Assets	$ 267		$ 267		$ 278
Contract Liabilities	789		789		824
Change in contract assets included in other current assets			(11)
Change in contracts liabilities included in deferred revenue			(35)
Current portion of contract assets	206		206		$ 204
Amounts included in the beginning of year contract liability balance	$ 41	$ 10	$ 724	$ 538

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.

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