Investigations, Claims, and Litigation (Narrative) (Details) $ in Millions	6 Months Ended
	Jun. 30, 2018 USD ($) frigates	Jun. 30, 2017 USD ($)
Bolivarian Republic of Venezuela
Loss Contingencies
Number of Foreign Built Frigates | frigates	2
Arbitral statement claim	$ 151.0
Litigation counter claim [Member] | Bolivarian Republic of Venezuela
Loss Contingencies
Arbitral statement claim	$ 22.0
Ingalls Timecharging Investigation
Loss Contingencies
Contract receivable retainage initially withheld		$ 24.0
United States Navy | Ingalls Timecharging Investigation
Loss Contingencies
Contract receivable retainage initially withheld		18.2
Contract Receivable Retainage		4.7
United States Coast Guard | Ingalls Timecharging Investigation
Loss Contingencies
Contract receivable retainage initially withheld		5.8
Contract Receivable Retainage		$ 3.6