Balance Sheet Accounts (Tables)

6 Months Ended

Jun. 30, 2018

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Schedule of Fair Value of Financial Instruments

The following are measured at fair value:

			Fair value measurement at June 30, 2018
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
	(In millions)
Money market funds	$	198.5	$	198.5	$	—	$	—
Commercial paper	119.8		—		119.8		—
	$	318.3	$	198.5	$	119.8	$	—
			Fair value measurement at December 31, 2017
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
	(In millions)
Money market funds	$	155.0	$	155.0	$	—	$	—
Commercial paper	135.6		—		135.6		—
U.S. treasury notes	4.1		—		4.1		—
	$	294.7	$	155.0	$	139.7	$	—

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:

	Fair Value				Principal Amount
	June 30, 2018		December 31, 2017		June 30, 2018		December 31, 2017
	(In millions)
Term loan	$	360.0	$	370.0	$	360.0	$	370.0
2 1/4% Notes	388.9		415.3		300.0		300.0
Capital leases	1.8		0.9		1.8		0.9
	$	750.7	$	786.2	$	661.8	$	670.9

Schedule of Accounts Receivable

Accounts Receivable

	June 30, 2018		December 31, 2017
	(In millions)
Billed receivables under long-term contracts	$	133.6	$	63.8
Other receivables	1.0		0.7
Accounts receivable	$	134.6	$	64.5

Schedule of Other Current Assets, net

Other Current Assets, net

	June 30, 2018		December 31, 2017
	(In millions)
Deferred costs recoverable from the U.S. government	$	45.3	$	51.4
Inventories	18.9		19.3
Receivable from Northrop Grumman Corporation (“Northrop”) for environmental remediation costs	6.0		6.0
Prepaid expenses	16.5		19.2
Cost-share and other receivables, net	7.1		7.5
Income taxes receivable	20.5		20.5
Other	8.9		5.2
Other current assets, net	$	123.2	$	129.1

Schedule of Property, Plant and Equipment, net

Property, Plant and Equipment, net

	June 30, 2018			December 31, 2017
	(In millions)
Land	$	71.2		$	71.2
Buildings and improvements	377.4			368.3
Machinery and equipment	492.5			493.2
Construction-in-progress	38.4			30.3
	979.5			963.0
Less: accumulated depreciation	(621.7		)	(604.0		)
Property, plant and equipment, net	$	357.8		$	359.0

Schedule of Other Noncurrent Assets, net

Other Noncurrent Assets, net

	June 30, 2018		December 31, 2017
	(In millions)
Real estate held for entitlement and leasing	$	94.9	$	94.0
Receivable from Northrop for environmental remediation costs	55.5		58.5
Deferred costs recoverable from the U.S. government	67.6		66.6
Grantor trusts	22.8		24.2
Notes receivable, net	9.0		9.0
Other	10.7		7.0
Other noncurrent assets, net	$	260.5	$	259.3

Schedule of Other Current Liabilities

Other Current Liabilities

	June 30, 2018		December 31, 2017
	(In millions)
Accrued compensation and employee benefits	$	104.2	$	113.4
Competitive improvement program obligations	14.6		15.0
Income taxes payable	136.4		0.8
Postretirement medical and life insurance benefits	4.8		4.8
Other program liabilities	33.2		6.6
Other	19.8		16.3
Other current liabilities	$	313.0	$	156.9

Schedule of Other Noncurrent Liabilities

Other Noncurrent Liabilities

	June 30, 2018		December 31, 2017
	(In millions)
Conditional asset retirement obligations	$	44.9	$	44.0
Pension benefits, non-qualified	17.2		17.6
Deferred compensation	29.3		29.4
Deferred revenue	12.4		12.7
Postretirement medical and life insurance benefits	31.4		32.7
Competitive improvement program obligations	13.7		18.4
Uncertain income tax positions	4.9		2.8
Other	20.9		13.5
Other noncurrent liabilities	$	174.7	$	171.1