Balance Sheet Accounts and Supplemental Disclosures (Tables)

12 Months Ended

Dec. 31, 2017

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Schedule of Short-term Available-for-sale Investments

As of December 31, 2017, the Company's short-term available-for-sale investments were as follows:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
	(In millions)
Commercial paper	$	135.6	$	—	$	—	$	135.6
U.S. treasury notes	4.1		—		—		4.1
Marketable securities	$	139.7	$	—	$	—	$	139.7

Schedule of Accounts Receivable

	As of December 31,
	2017			2016
	(In millions)
Billed	$	62.1		$	55.7
Unbilled	195.5			124.1
Reserve for overhead rate disallowance	(42.8		)	(44.5		)
Total receivables under long-term contracts	214.8			135.3
Other receivables	0.7			1.1
Accounts receivable	$	215.5		$	136.4

Schedule of Inventories

	As of December 31,
	2017			2016
	(In millions)
Long-term contracts at average cost	$	562.3		$	551.9
Progress payments	(427.1		)	(368.2		)
Total long-term contract inventories	135.2			183.7
Total other inventories	1.2			1.4
Inventories	$	136.4		$	185.1

Schedule of Other Current Assets, net

	As of December 31,
	2017		2016
	(In millions)
Recoverable from the U.S. government for acquisition integration costs	$	10.9	$	11.9
Recoverable from the U.S. government and other third parties for environmental remediation costs	25.6		25.2
Receivable from Northrop for environmental remediation costs	6.0		6.0
Prepaid expenses	19.2		16.5
Cost-share and other receivables, net	7.5		17.8
Recoverable from the U.S. government for competitive improvement program obligations	14.9		7.6
Income tax receivable	20.5		26.8
Other	5.2		11.1
Other current assets, net	$	109.8	$	122.9

Schedule of Property, Plant and Equipment, net

	As of December 31,
	2017			2016
	(In millions)
Land	$	71.2		$	71.4
Buildings and improvements	368.3			345.1
Machinery and equipment	493.2			499.9
Construction-in-progress	30.3			30.4
	963.0			946.8
Less: accumulated depreciation	(604.0		)	(580.8		)
Property, plant and equipment, net	$	359.0		$	366.0

Schedule of Intangible Assets

	As of December 31, 2017
	Gross Carrying Amount		Accumulated Amortization		Net Carrying Amount
	(In millions)
Customer related	$	87.2	$	46.9	$	40.3
Intellectual property\trade secrets	34.2		11.8		22.4
Trade name	21.0		3.1		17.9
Acquired technology	19.2		14.3		4.9
Intangible assets	$	161.6	$	76.1	$	85.5

	As of December 31, 2016
	Gross Carrying Amount		Accumulated Amortization		Net Carrying Amount
	(In millions)
Customer related	$	83.8	$	37.4	$	46.4
Intellectual property\trade secrets	34.2		9.2		25.0
Non-compete agreements	0.5		0.5		—
Trade name	20.5		2.4		18.1
Acquired technology	18.3		13.4		4.9
Intangible assets	$	157.3	$	62.9	$	94.4

Schedule of Future Amortization Expense for Intangible Assets

Future amortization expense for the five succeeding years is estimated to be as follows:

Year Ending December 31,	Future Amortization Expense
	(In millions)
2018	$	13.7
2019	13.6
2020	13.4
2021	9.9
2022	6.6
	$	57.2

Schedule of Other Noncurrent Assets, net

	As of December 31,
	2017		2016
	(In millions)
Real estate held for entitlement and leasing	$	94.0	$	91.8
Receivable from Northrop for environmental remediation costs	58.5		62.0
Recoverable from the U.S. government for acquisition integration costs	—		10.9
Recoverable from the U.S. government for conditional asset retirement obligations	22.7		20.3
Recoverable from the U.S. government for competitive improvement program obligations	18.4		1.3
Recoverable from the U.S. government for restructuring costs	25.5		12.8
Grantor trust	24.2		16.6
Note receivable, net	9.0		9.0
Income tax receivable	—		10.8
Other	7.0		8.5
Other noncurrent assets, net	$	259.3	$	244.0

Schedule of Other Current Liabilities

	As of December 31,
	2017		2016
	(In millions)
Accrued compensation and employee benefits	$	113.4	$	105.7
Contract related liabilities	41.7		24.7
Income taxes	0.8		2.1
Competitive improvement program obligations	15.0		7.6
Postretirement medical and life insurance benefits	4.8		5.2
Interest payable	0.6		4.1
Contract loss provisions	3.8		6.8
Other	15.8		16.8
Other current liabilities	$	195.9	$	173.0

Schedule of Other Noncurrent Liabilities

	As of December 31,
	2017		2016
	(In millions)
Conditional asset retirement obligations	$	44.0	$	30.6
Pension benefits, non-qualified	17.6		17.5
Deferred compensation	29.4		19.8
Deferred revenue	12.7		13.3
Postretirement medical and life insurance benefits	32.7		37.4
Competitive improvement program obligations	18.4		1.3
Uncertain income tax positions	2.8		28.4
Other	13.5		13.1
Other noncurrent liabilities	$	171.1	$	161.4

Schedule of Accumulated Other Comprehensive Loss, Net of Income Taxes

Changes in accumulated other comprehensive loss by components, net of income taxes:

	Actuarial Losses, Net			Prior Service Credits, Net			Total
	(In millions)
November 30, 2015	$	(342.6	)	$	0.9		$	(341.7	)
Actuarial losses arising during the period, net of income taxes	(8.6		)	—			(8.6		)
Amortization of actuarial losses and prior service credits, net of income taxes	3.4			(0.1		)	3.3
December 31, 2015	(347.8		)	0.8			(347.0		)
Actuarial gains arising during the period, net of income taxes	7.5			—			7.5
Amortization of actuarial losses and prior service credits, net of income taxes	37.1			(0.6		)	36.5
December 31, 2016	(303.2		)	0.2			(303.0		)
Actuarial losses arising during the period, net of income taxes	(8.5		)	—			(8.5		)
Amortization of actuarial losses and prior service credits, net of income taxes	39.0			(0.1		)	38.9
December 31, 2017	$	(272.7	)	$	0.1		$	(272.6	)

Schedule of Estimated Amounts to be Amortized from Other Comprehensive Loss to Net Periodic Benefit Expense

The estimated amounts that will be amortized from accumulated other comprehensive loss into net periodic benefit expense in fiscal 2018:

	Pension Benefits		Medical and Life Insurance Benefits
	(In millions)
Actuarial losses (gains), net	$	70.7	$	(3.7	)
Prior service costs (credits), net	0.1		(0.2		)
	$	70.8	$	(3.9	)