Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Details 5) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue, Major Customer [Line Items]
Total sales	$ 6,634	$ 6,527	$ 6,375	$ 6,267	$ 6,397	$ 6,155	$ 6,000	$ 5,956	$ 25,803	$ 24,508	$ 23,526
US Government [Member]
Revenue, Major Customer [Line Items]
Total sales									$ 21,837	$ 20,573	$ 19,458
Concentration Risk, Percentage									85.00%	84.00%	83.00%
International Customer [Member]
Revenue, Major Customer [Line Items]
Total sales									$ 3,302	$ 3,205	$ 3,339
Concentration Risk, Percentage									13.00%	13.00%	14.00%
Other Customers [Member]
Revenue, Major Customer [Line Items]
Total sales									$ 664	$ 730	$ 729
Concentration Risk, Percentage									2.00%	3.00%	3.00%