Basis of Presentation and Significant Accounting Policies and Practices - Additional Information (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jan. 01, 2018
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Antidilutive securities excluded from computation of earnings per share, Amount (in shares)	5	6	5	6
ASU 2014-09
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Contract asset	$ 275		$ 275
Revenue remaining performance obligation	72		$ 72
Revenue remaining performance obligation of percentage rate			22.00%
Revenue, remaining performance obligation, expected timing of satisfaction, period			12 months
Contract asset reduction	$ 8		$ 8
Contract asset due to cash received			16
Contract of income recognized			$ 8
ASU 2014-09 | Cumulative Impact of Adopting ASC 606
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Cumulative impact of retained earnings, net of taxes					$ 206
Contract asset					283
Deferred tax liabilities					$ 55