Summary of Significant Accounting Policies Backlog and Contract Assets and Liabilities (Details 5) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Revenue, Remaining Performance Obligation, Amount	$ 81,000
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Explanation	We expect to recognize approximately 40 percent and 60 percent of our December 31, 2020 backlog as revenue over the next 12 and 24 months, respectively, with the remainder to be recognized thereafter.
Unbilled Receivables, Current	$ 5,140	$ 5,334
Amount of increase (decrease) in Unbilled Receivables	$ (194)
Percent increase (decrease) in Unbilled Receivables	(4.00%)
Contract with Customer, Liability, Current	$ (2,517)	(2,237)
Amount of decrease (increase) in Contract with Customer, Liability, Current	$ (280)
Percent decrease (increase) in Contract with Customer, Liability, Current	13.00%
Contract with Customer, Asset, Net, Current	$ 2,623	3,097
Amount of increase (decrease) in net contract assets (liabilities)	$ (474)
Percent increase (decrease) in net contract assets (liabilities)	(15.00%)
Contract with Customer, Liability, Revenue Recognized	$ 1,600	$ 1,300	$ 1,300