Balance Sheet Accounts (Tables)

6 Months Ended

Jun. 30, 2020

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Schedule of Fair Value of Financial Instruments

			Fair value measurement as of June 30, 2020
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Other Observable Inputs (Level 2)		Unobservable Inputs (Level 3)
	(In millions)
Money market funds	$	570.0	$	570.0	$	—	$	—
Registered investment companies	3.0		3.0		—		—
Commercial paper	110.0		—		110.0		—
Total	$	683.0	$	573.0	$	110.0	$	—

			Fair value measurement as of December 31, 2019
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Other Observable Inputs (Level 2)		Unobservable Inputs (Level 3)
	(In millions)
Money market funds	$	626.0	$	626.0	$	—	$	—
Registered investment companies	3.7		3.7		—		—
Commercial paper	99.9		—		99.9
Total	$	729.6	$	629.7	$	99.9	$	—

Schedule of Estimated Fair Value and Principal Amount of Outstanding Debt

The following table summarizes the estimated fair value and principal amount for outstanding debt obligations excluding finance lease obligations:

	Fair Value				Principal Amount
	June 30, 2020		December 31, 2019		June 30, 2020		December 31, 2019
	(In millions)
Term loan	$	303.4	$	328.1	$	319.4	$	328.1
21/4% Notes	477.4		546.0		300.0		300.0
Total	$	780.8	$	874.1	$	619.4	$	628.1

Schedule of Accounts Receivable

Accounts Receivable, net

	June 30, 2020			December 31, 2019
	(In millions)
Billed receivables under long-term contracts	$	81.0		$	122.9
Reserve on billed trade receivables	(1.0		)	(10.6		)
Other trade receivables	0.4			0.2
Accounts receivable, net	$	80.4		$	112.5

Schedule of Other Current Assets, net

Other Current Assets, net

	June 30, 2020		December 31, 2019
	(In millions)
Deferred costs recoverable from the U.S. government	$	45.7	$	47.1
Income taxes receivable	23.7		43.4
Inventories	15.8		24.0
Prepaid expenses	15.2		13.9
Other	13.8		17.4
Other current assets, net	$	114.2	$	145.8

Schedule of Property, Plant and Equipment, net

Property, Plant and Equipment, net

	June 30, 2020			December 31, 2019
	(In millions)
Land	$	71.2		$	71.2
Buildings and improvements	439.6			434.9
Machinery and equipment, including capitalized software	461.8			488.2
Construction-in-progress	72.1			70.2
	1,044.7			1,064.5
Less: accumulated depreciation	(643.2		)	(654.6		)
Property, plant and equipment, net	$	401.5		$	409.9

Schedule of Other Noncurrent Assets, net

Other Noncurrent Assets, net

	June 30, 2020		December 31, 2019
	(In millions)
Real estate held for entitlement and leasing	$	100.7	$	100.3
Deferred costs recoverable from the U.S. government	56.3		54.8
Receivable from Northrop Grumman Corporation for environmental remediation costs	43.5		46.5
Other	47.6		54.0
Other noncurrent assets, net	$	248.1	$	255.6

Schedule of Other Current Liabilities

Other Current Liabilities

	June 30, 2020		December 31, 2019
	(In millions)
Accrued compensation and employee benefits	$	105.2	$	103.1
Other	42.5		52.4
Other current liabilities	$	147.7	$	155.5