Revenue - Contract Balances (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Contract Assets (Unearned Income)
Current contract assets	$ 166		$ 166		$ 155
Long-term contract assets	16		16		10
Current unearned income	(112)		(112)		(108)
Long-term unearned income	(20)		(20)		(21)
Net Contract Assets (Unearned Income)	50		50		36
Accounts receivable, net	687		687		$ 652
Revenue recognized	$ 20	$ 16	$ 84	$ 97