Balance Sheet Accounts (Tables)

3 Months Ended

Mar. 31, 2020

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Schedule of Fair Value of Financial Instruments

			Fair value measurement as of March 31, 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	$	652.9	$	652.9	$	—	$	—
Registered investment companies	3.3		3.3		—		—
Commercial paper	15.0		—		15.0		—
Total	$	671.2	$	656.2	$	15.0	$	—

			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
	March 31, 2020		December 31, 2019		March 31, 2020		December 31, 2019
	(In millions)
Term loan	$	299.9	$	328.1	$	323.8	$	328.1
21/4% Notes	488.2		546.0		300.0		300.0
Total	$	788.1	$	874.1	$	623.8	$	628.1

Schedule of Accounts Receivable

Accounts Receivable, net

	March 31, 2020			December 31, 2019
	(In millions)
Billed receivables under long-term contracts	$	152.5		$	122.9
Reserve on billed trade receivables	(1.0		)	(10.6		)
Other trade receivables	0.2			0.2
Accounts receivable, net	$	151.7		$	112.5

Schedule of Other Current Assets, net

Other Current Assets, net

	March 31, 2020		December 31, 2019
	(In millions)
Deferred costs recoverable from the U.S. government	$	46.9	$	47.1
Income taxes receivable	36.2		43.4
Inventories	18.0		24.0
Prepaid expenses	13.4		13.9
Other	22.9		17.4
Other current assets, net	$	137.4	$	145.8

Schedule of Property, Plant and Equipment, net

Property, Plant and Equipment, net

	March 31, 2020			December 31, 2019
	(In millions)
Land	$	71.2		$	71.2
Buildings and improvements	436.2			434.9
Machinery and equipment, including capitalized software	459.4			488.2
Construction-in-progress	67.1			70.2
	1,033.9			1,064.5
Less: accumulated depreciation	(630.7		)	(654.6		)
Property, plant and equipment, net	$	403.2		$	409.9

Schedule of Other Noncurrent Assets, net

Other Noncurrent Assets, net

	March 31, 2020		December 31, 2019
	(In millions)
Real estate held for entitlement and leasing	$	100.4	$	100.3
Deferred costs recoverable from the U.S. government	55.9		54.8
Receivable from Northrop Grumman Corporation for environmental remediation costs	45.0		46.5
Other	50.2		54.0
Other noncurrent assets, net	$	251.5	$	255.6

Schedule of Other Current Liabilities

Other Current Liabilities

	March 31, 2020		December 31, 2019
	(In millions)
Accrued compensation and employee benefits	$	90.0	$	103.1
Other	44.4		52.4
Other current liabilities	$	134.4	$	155.5