Revenue from Contracts with Customers - Estimate at Completion Adjustments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Change in Accounting Estimate [Line Items]
Revenue	$ 720	$ 719	$ 2,059	$ 1,952
Contracts Accounted for under Percentage of Completion
Change in Accounting Estimate [Line Items]
Revenue	$ (11)	$ (30)	$ (20)	$ (63)
Total % of Revenue	1.60%	4.20%	1.00%	3.20%