Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Details 6) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenue, Major Customer [Line Items]
Total sales	$ 6,397	$ 6,155	$ 6,000	$ 5,956	$ 5,694	$ 5,979	$ 5,896	$ 5,957	$ 24,508	$ 23,526	$ 23,979
US Government [Member]
Revenue, Major Customer [Line Items]
Total sales									$ 20,573	$ 19,458	$ 20,085
Concentration Risk, Percentage									84.00%	83.00%	84.00%
International Customer [Member]
Revenue, Major Customer [Line Items]
Total sales									$ 3,205	$ 3,339	$ 3,045
Concentration Risk, Percentage									13.00%	14.00%	13.00%
Other Customers [Member]
Revenue, Major Customer [Line Items]
Total sales									$ 730	$ 729	$ 849
Concentration Risk, Percentage									3.00%	3.00%	3.00%