2018 Impact of Accounting Method Change (Details 3) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net Income (Loss) Attributable to Parent	$ 356	$ 1,244	$ 789	$ 840	$ 672	$ 750	$ 677	$ 770	$ 3,229	$ 2,869	$ 2,043
Depreciation, Depletion and Amortization									800	475	456
Mark-to-market pension and OPEB Benefit									655	(536)	950
Deferred income taxes									234	985	(60)
Stock-based compensation									86	94	93
Accounts receivable, net									202	(209)	46
Unbilled receivables, net									(297)	(422)	(211)
Inventoried costs, net									(37)	25	(53)
Prepaid expenses and other assets									(56)	(92)	(117)
Accounts payable and other liabilities									381	570	18
Retiree benefits									(1,083)	(946)	(375)
Other, net									(29)	(43)	(125)
Income taxes payable, net									(258)	(157)	148
Net cash provided by operating activities									3,827	2,613	2,813
Adjustments for change to Defined Benefit Plan, Actuarial Gain (Loss), Immediate Recognition as Component in Net Period Benefit (Cost) [Member] | Adjustments for Change in Accounting Principle [Domain]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net Income (Loss) Attributable to Parent	$ (394)	$ 100	$ 100	$ 101	$ 525	$ 107	$ 122	$ 120	(93)	874	(113)
Depreciation, Depletion and Amortization									0	0	0
Mark-to-market pension and OPEB Benefit									(655)
Deferred income taxes									(29)	417	(69)
Stock-based compensation									0	0	0
Accounts receivable, net									0	0	0
Unbilled receivables, net									0	0	0
Inventoried costs, net									0	0	0
Prepaid expenses and other assets									0	0	0
Accounts payable and other liabilities									0	0	0
Retiree benefits									(533)	(755)	(768)
Other, net									0	0	0
Income taxes payable, net									0	0	0
Net cash provided by operating activities									0	0	0
Method Prior to change to Defined Benefit Plan, Actuarial Gain (Loss), Immediate Recognition as Component in Net Period Benefit (Cost) [Member] [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net Income (Loss) Attributable to Parent									3,322
Depreciation, Depletion and Amortization									800
Mark-to-market pension and OPEB Benefit									0
Deferred income taxes									263
Stock-based compensation									86
Accounts receivable, net									202
Unbilled receivables, net									297
Inventoried costs, net									(37)
Prepaid expenses and other assets									(56)
Accounts payable and other liabilities									381
Retiree benefits									(550)
Other, net									(29)
Income taxes payable, net									(258)
Net cash provided by operating activities									$ 3,827
Retained Earnings [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net Income (Loss) Attributable to Parent										2,869	2,043
Retained Earnings [Member] | Adjustments for change to Defined Benefit Plan, Actuarial Gain (Loss), Immediate Recognition as Component in Net Period Benefit (Cost) [Member] | Adjustments for Change in Accounting Principle [Domain]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net Income (Loss) Attributable to Parent										$ 874	$ (113)