Basis of Presentation - Shared Services Arrangement (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended	9 Months Ended
	Mar. 31, 2019	Sep. 30, 2019	Sep. 30, 2019
Long-term Purchase Commitment [Line Items]
Shared services arrangement, transition period	18 months
Shared services arrangement, commitment amount			$ 1,300
Shared services arrangement, period			7 years
Shared Services Arrangement with HCL Technologies | Employee Transfers
Long-term Purchase Commitment [Line Items]
Shared services arrangement, net charges incurred		$ 38	$ 68