Contracts with Customers Contracts with Customers (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Schedule of Contract Assets and Liabilities [Line Items]
Unbilled receivables, net	$ 7,995	$ 9,043
Contract with Customer, Asset, Explanation of Change	primarily driven by an increase in billings at BDS and BGS, as well as an increase in allowances for expected credit losses at BGS.
Advances and progress billings	$ 50,488	51,551
Contract with Customer, Liability, Explanation of Change	primarily driven by revenue recognized in excess of advances on orders received and return of BCA customer advances, partially offset by advances on orders received at BCA, BDS, and BGS
Contract with Customer, Liability, Revenue Recognized	$ 10,360	16,778
Commercial Customers
Schedule of Contract Assets and Liabilities [Line Items]
Unbilled receivables, expected to be collected after one year	$ 178	$ 211