Summary of Significant Accounting Policies Balance sheet Items (Details) - USD ($) $ in Millions	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Contract assets	$ 1,590	$ 1,349	$ 0
Contracts in process	0	0	1,933
Inventories	879	926	389
Prepaid Expense and Other Assets	356	317
Assets Held-for-sale, Not Part of Disposal Group, Current	0	138	135	$ 0
Assets of discontinued operations	0	285	306	481
Assets, Current	4,810	4,400	4,448
Other assets	341	313	264
Total Assets	13,518	12,730	12,729	11,865
Accrued expenses	251	204	217
Contract liabilities	669	565	0
Advance payments and billings in excess of costs incurred	0	0	509
Income taxes payable	49		19
Other current liabilities	288	318	367
Liabilities held for sale	0	16	17
Liabilities of discontinued operations	0	203	226
Liabilities, Current	2,447	2,349	2,379
Deferred income taxes	196	162	158
Other liabilities	436	412	398
Liabilities	7,611	7,566	7,578
Retained earnings	7,424	6,672	6,659
Total equity	5,907	5,164	5,151	$ 4,624	$ 4,429
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Contract assets	1,590	1,349
Contracts in process	(2,127)	(1,933)
Inventories	486	537
Prepaid Expense and Other Assets	16	17
Assets Held-for-sale, Not Part of Disposal Group, Current		3
Assets of discontinued operations		(21)
Assets, Current	(35)	(48)
Other assets	46	49
Total Assets	11	1
Accrued expenses	(24)	(13)
Contract liabilities	669	565
Advance payments and billings in excess of costs incurred	(604)	(509)
Income taxes payable	(4)
Other current liabilities	(76)	(49)
Liabilities held for sale		(1)
Liabilities of discontinued operations		(23)
Liabilities, Current	(39)	(30)
Deferred income taxes	11	4
Other liabilities	14	14
Liabilities	(14)	(12)
Retained earnings	25	13
Total equity	25	$ 13
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Contract assets	0		0
Contracts in process	2,127		1,933
Inventories	393		389
Prepaid Expense and Other Assets	340		300
Assets Held-for-sale, Not Part of Disposal Group, Current			135
Assets of discontinued operations			306
Assets, Current	4,845		4,448
Other assets	295		264
Total Assets	13,507		12,729
Accrued expenses	275		217
Contract liabilities	0		0
Advance payments and billings in excess of costs incurred	604		509
Income taxes payable	53
Other current liabilities	364		367
Liabilities held for sale			17
Liabilities of discontinued operations			226
Liabilities, Current	2,486		2,379
Deferred income taxes	185		158
Other liabilities	422		398
Liabilities	7,625		7,578
Retained earnings	7,399		6,659
Total equity	$ 5,882		$ 5,151