Acquisitions and Divestitures, Goodwill, and Intangible Assets (Intangible Assets) (Details) - USD ($) $ in Millions		Dec. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	[1]	$ 4,210	$ 4,573
Accumulated Amortization		(2,093)	(2,258)
Net Carrying Amount		2,117	2,315	[2]
Contract and Program Intangible Assets
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	[1],[3]	3,399	3,776
Accumulated Amortization	[3]	(1,600)	(1,779)
Net Carrying Amount		1,799	1,997
Tradenames and Trademarks
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	[1]	516	474
Accumulated Amortization		(229)	(195)
Net Carrying Amount		287	279
Technology and Software
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	[1]	134	164
Accumulated Amortization		(106)	(126)
Net Carrying Amount		28	38
Other Intangible Assets
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	[1]	161	159
Accumulated Amortization		(158)	(158)
Net Carrying Amount		$ 3	$ 1

[1] Changes in gross carrying amounts consist primarily of adjustments for write-offs of fully amortized intangible assets, acquired intangible assets and foreign currency translation.

[2] *Prior-period information has been restated for the retrospective application of a change in accounting principle related to the amortization of actuarial gains and losses for our qualified U.S. government pension plans, which we adopted in the fourth quarter of 2020. For further discussion of this change in accounting principle, see Note T to the Consolidated Financial Statements.

[3] Consists of acquired backlog and probable follow-on work and associated customer relationships.