Segment Information - Revenues and Intersegment Revenues (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Segment Reporting Information [Line Items]
Revenue	$ 720	$ 719	$ 2,059	$ 1,952
Operating Segments | AST
Segment Reporting Information [Line Items]
Revenue	279	263	743	668
Operating Segments | NC&C
Segment Reporting Information [Line Items]
Revenue	239	267	747	749
Operating Segments | IMS
Segment Reporting Information [Line Items]
Revenue	209	194	584	553
Total intersegment revenue
Segment Reporting Information [Line Items]
Revenue	(7)	(4)	(15)	(18)
Total intersegment revenue | AST
Segment Reporting Information [Line Items]
Revenue	2	2	5	10
Total intersegment revenue | NC&C
Segment Reporting Information [Line Items]
Revenue	5	2	10	7
Total intersegment revenue | IMS
Segment Reporting Information [Line Items]
Revenue	$ 0	$ 0	$ 0	$ 1