Segment Information - Depreciation and Assets (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Depreciation	$ 12	$ 11
Assets	2,914		$ 2,956
AST
Segment Reporting Information [Line Items]
Depreciation	5	5
NC&C
Segment Reporting Information [Line Items]
Depreciation	3	3
IMS
Segment Reporting Information [Line Items]
Depreciation	4	$ 3
Operating Segments | AST
Segment Reporting Information [Line Items]
Assets	908		862
Operating Segments | NC&C
Segment Reporting Information [Line Items]
Assets	719		691
Operating Segments | IMS
Segment Reporting Information [Line Items]
Assets	1,015		963
Corporate & Eliminations
Segment Reporting Information [Line Items]
Assets	$ 272		$ 440