Revenue - Contract Balances (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Contract Assets (Unearned Income)
Current contract assets	$ 160		$ 160		$ 155
Long-term contract assets	16		16		10
Current unearned income	(106)		(106)		(108)
Long-term unearned income	(22)		(22)		(21)
Net Contract Assets (Unearned Income)	48		48		36
Accounts receivable, net	693		693		$ 652
Revenue recognized	$ 22	$ 28	$ 64	$ 81

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.

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