Contract Assets and Liabilities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Contract with Customer, Asset and Liability [Abstract]
Current Contract Assets, Net	$ 458	$ 396
Current Contract Liabilities	909	805	$ 0
Noncurrent Contract Liability	317	$ 302
Revenue recognized that was included in the current contract liability balance at the beginning of the period	$ 308