Revenue from Contract with Customer (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 28, 2019	Dec. 29, 2018
Revenue from Contract with Customer [Abstract]
Segment Reporting, Disclosure of Major Customers	Revenues attributable to our relationships (as the prime contractor or a subcontractor) with U.S. government agencies, within our Domestic segment, comprised 18% and 13% of our consolidated revenues for 2020 and 2019, respectively. Amounts due in connection with these relationships comprised 13% of client receivables as of December 31, 2020.
Contract with Customer, Liability, Explanation of Change	substantially all of our contract liability balance at the beginning of each respective year was recognized in revenues during that year
Capitalized Contract Cost, Net	$ 88	$ 89
Capitalized Contract Cost, Amortization	$ 38	$ 41	$ 41
Revenue, Judgment	Our contracts with clients typically include various combinations of our software solutions and related services. Determining whether such software solutions and services are considered distinct performance obligations that should be accounted for separately versus together may require significant judgment
Revenue, Information Used to Allocate Transaction Price	Contract transaction price is allocated to distinct performance obligations using estimated stand-alone selling price
Revenue, Information Used to Determine Transaction Price	We determine stand-alone selling price maximizing observable inputs such as stand-alone sales when they exist or substantive renewal prices charged to clients. In instances where stand-alone selling price is not observable, we utilize an estimate of stand-alone selling price. Such estimates are derived from various methods that include: cost plus margin, historical pricing practices, and the residual approach. Judgment may be required to determine standalone selling prices for each performance obligation and whether it depicts the amount we expect to receive in exchange for the related good or service.
Revenue, Practical Expedient, Initial Application and Transition, Nonrestatement of Modified Contract [true false]			true