Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Change in Accounting Estimate [Line Items]

Schedule of Fair Value of Financial Instruments

The following are measured at fair value:

			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		—
Total	$	294.7	$	155.0	$	139.7	$	—
			Fair value measurement at December 31, 2016
	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	$	328.5	$	328.5	$	—	$	—

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
	December 31, 2017		December 31, 2016		December 31, 2017		December 31, 2016
	(In millions)
Term loan	$	370.0	$	390.0	$	370.0	$	390.0
2.25% Convertible Senior Notes ("2 1/4% Notes")	415.3		294.9		300.0		300.0
4 1/16% Convertible Subordinated Debentures (“4 1/16% Debentures”)	—		70.8		—		35.6
Capital leases	0.9		—		0.9		—
	$	786.2	$	755.7	$	670.9	$	725.6

Schedule of Useful Lives of Property, Plant and Equipment

Depreciation is computed principally by accelerated methods based on the following useful lives:

Buildings and improvements	3 - 40  years
Machinery and equipment	6 - 10  years

Schedule of Changes in Carrying Amount of Conditional Asset Retirement Obligations

The changes in the carrying amount of CAROs since November 30, 2014 were as follows (in millions):

Balance as of November 30, 2014	$	24.4
Additions and other, net	3.0
Accretion	1.9
Balance as of November 30, 2015	29.3
Accretion	0.2
Balance as of December 31, 2015	29.5
Additions and other, net	(0.9		)
Accretion	2.0
Balance as of December 31, 2016	30.6
Additions and other, net	11.2
Accretion	2.2
Balance as of December 31, 2017	$	44.0

AR1 Inception to Date Project Costs

The AR1 inception to date project costs at December 31, 2017, were as follows (in millions):

AR1 R&D costs incurred	$	245.6
Less amounts funded by the U.S. Air Force	(147.7		)
Less amounts funded by ULA	(9.7		)
AR1 R&D costs net of reimbursements	$	88.2

Schedule of Land Sale on the Consolidated Statement of Operations

A summary of the impact of the land sale on the consolidated statement of operations for fiscal 2015 was as follows (in millions):

Net sales from land sale	$	42.0
Cost of sales from land sale	11.4
Income before income taxes from land sale	30.6
Income tax provision related to land sale	12.7
Net income from land sale	$	17.9

Schedule of Sales to U.S. Government and its Agencies

Sales to the U.S. government and its agencies, including sales to the Company’s significant customers discussed below, were as follows:

	Percentage of Net Sales
Fiscal 2017	92	%
Fiscal 2016	91	%
Fiscal 2015	90	%
One month ended December 31, 2015	85	%

Schedules of Percentage of Net Sales for Significant Programs

The following are percentages of net sales for significant programs, all of which are included in the U.S. government sales and are comprised of multiple contracts.

	Year Ended						One month ended
	December 31,		December 31,		November 30,		December 31,
	2017		2016		2015		2015
RS-25 program	14	%	12	%	12	%	10	%
Standard Missile program	9		12		14		12
THAAD program	9		13		13		13

Schedule of Customers that Represented More than 10% of Net Sales

Customers that represented more than 10% of net sales for the periods presented were as follows:

	Year Ended						One month ended
	December 31,		December 31,		November 30,		December 31,
	2017		2016		2015		2015
Lockheed Martin Corporation ("Lockheed Martin")	24	%	27	%	29	%	24	%
ULA	22		21		19		28
Raytheon Company ("Raytheon")	17		20		20		19
NASA	17		13		11		10

Schedule of Customers that Represented More than 10% of Accounts Receivable

Customers that represented more than 10% of accounts receivable for the periods presented were as follows:

	As of December 31,
	2017		2016
The Boeing Company ("Boeing")	35	%	13	%
Raytheon	16		17
Lockheed Martin	12		17
NASA	11		14
ULA	11		20

Contracts Accounted for under Percentage-of-Completion

Change in Accounting Estimate [Line Items]

Summary of Impact of Contracts in Progress on Statement of Operations

The following table summarizes the impact of the change in significant contract accounting estimates on the Company’s Aerospace and Defense segment operating results accounted for under the percentage-of-completion method of accounting:

	Year Ended						One month ended
	December 31,		December 31,		November 30,		December 31,
	2017		2016		2015		2015
	(In millions, except per share amounts)
Favorable effect of the changes in contract estimates on income (loss) before income taxes	$	37.2	$	14.1	$	41.2	$	11.7
Favorable effect of the changes in contract estimates on net (loss) income	22.3		8.5		24.7		7.0
Favorable effect of the changes in contract estimates on basic net (loss) income per share	0.31		0.13		0.40		0.11
Favorable effect of the changes in contract estimates on diluted net (loss) income per share	0.31		0.11		0.40		0.09