Summary of Significant Accounting Policies Update - Contracts accounted for under cumulative catch-up method (Details) - Cumulative catch-up method - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017
Use of Estimates
Cumulative Catch-Up Adjustments	$ 64	$ 9	$ 104	$ (3)
Change in Accounting Estimate Financial Effect Increase (Decrease) In Income From Continuing Operations Before Income Taxes	64	9	104	(3)
Change in Accounting Estimate Financial Effect Increase (Decrease) In Income From Continuing Operations After Income Taxes	$ 49	$ 6	$ 79	$ (2)
Change In Accounting Estimate Financial Effect Increase (Decrease) In Earnings Per Share Diluted	$ 0.19	$ 0.02	$ 0.30	$ (0.01)
Gross favorable adjustments	$ 70	$ 23	$ 126	$ 43
Gross unfavorable adjustments	$ 6	$ 14	$ 22	$ 46