Amount of revenue recognized from performance obligation satisfied or partially satisfied in previous reporting periods. Includes, but is not limited to, change in transaction price.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Revenue (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
Revenue (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue from Contract with Customer [Abstract]
Revenue recognized from performance obligations	$ 15
Disaggregation of Revenue [Line Items]
Revenues	5,639	$ 4,913	$ 4,171
Government Solutions \| Key U.S. Government Customers
Disaggregation of Revenue [Line Items]
Revenues	3,000	2,600
Government Solutions \| Non U.S. Government Customers
Disaggregation of Revenue [Line Items]
Revenues	$ 911	$ 847