Restatement - Schedule of Effects of Prior Period Errors on the Consolidated Financial Statements - Consolidated Balance Sheet (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015	Nov. 30, 2015	Feb. 28, 2015	Nov. 30, 2014
Current Assets
Cash and cash equivalents	$ 155.5	$ 208.5	$ 211.1	$ 215.7	$ 265.9
Accounts receivable	182.3	169.5	171.5	190.0
Inventories	170.6	156.2	157.5	161.5
Recoverable from the U.S. government and other third parties for environmental remediation costs	27.1	24.0	24.0	23.5
Other current assets, net	70.8	69.2	64.4	43.7
Income taxes	1.6	1.6	2.9	2.3
Deferred income taxes	36.7	36.5	28.1	18.7
Total Current Assets	649.0	669.9	662.6	661.4
Noncurrent Assets
Property, plant and equipment, net	359.4	363.3	365.8	357.2
Real estate held for entitlement and leasing	87.3	86.2	86.2	81.5
Recoverable from the U.S. government and other third parties for environmental remediation costs	201.9	207.2	210.4	79.3
Deferred income taxes	286.2	288.3	286.7	256.0
Goodwill	158.1	158.1	158.1	158.1
Intangible assets	104.3	107.7	108.8	118.8
Assets held for sale				14.2
Other noncurrent assets, net	79.1	81.6	82.0	84.9
Total Noncurrent Assets	1,339.0	1,355.6	1,360.7	1,219.4
Total Assets	1,988.0	2,025.5	2,023.3	1,880.8
Current Liabilities
Short-term borrowings and current portion of long-term debt, net of deferred financing costs	5.2	5.3	5.3	5.2
Accounts payable	86.7	64.2	105.2	85.0
Reserves for environmental remediation costs	37.1	32.6	32.6	38.3
Postretirement medical and life insurance benefits	6.0	6.0	6.0	6.4
Advance payments on contracts	200.8	230.9	203.7	207.0
Other current liabilities	180.5	203.1	201.3	213.5
Total Current Liabilities	516.3	542.1	554.1	555.4
Noncurrent Liabilities
Senior debt, net of deferred financing costs	85.6	86.8	88.1	91.6
Total senior secured notes	450.0	449.4	449.4	448.2
Convertible subordinated debentures, bearing interest at 4.0625% per annum, interest payments due in June and December, maturing in December 2039	84.8	84.8	84.8	99.4
Other debt, net of deferred financing costs	0.0	12.7	12.8	79.2
Reserves for environmental remediation costs	262.2	269.7	273.5	124.3
Pension benefits	575.0	580.6	566.2	479.1
Postretirement medical and life insurance benefits	44.1	44.8	45.5	50.6
Other noncurrent liabilities	94.0	95.2	94.4	81.8
Total Noncurrent Liabilities	1,595.7	1,624.0	1,614.7	1,454.2
Total Liabilities	2,112.0	2,166.1	2,168.8	2,009.6
Redeemable common stock, par value of $0.10; 0.1 million shares issued and outstanding as of March 31, 2016, December 31, 2015, and November 30, 2015	1.3	1.6	0.9	0.1
Stockholders’ Deficit
Common stock	6.5	6.5	6.5	6.3
Other capital	345.3	342.6	340.1	324.6
Treasury stock	(64.5)	(64.5)	(64.5)	(64.5)
Accumulated deficit	(74.7)	(79.8)	(86.8)	(73.9)
Accumulated other comprehensive loss, net of income taxes	(337.9)	(347.0)	(341.7)	(321.4)
Total Stockholders’ Deficit	(125.3)	(142.2)	(146.4)	(128.9)
Total Liabilities, Redeemable Common Stock and Stockholders’ Deficit	1,988.0	2,025.5	2,023.3	1,880.8
Northrop [Member]
Current Assets
Receivable from Northrop	6.0	6.0	6.0	6.0
Noncurrent Assets
Receivable from Northrop	$ 62.7	$ 63.2	$ 62.7	69.4
As Reported [Member]
Current Assets
Cash and cash equivalents				215.7	265.9
Accounts receivable				206.1
Inventories				161.4
Recoverable from the U.S. government and other third parties for environmental remediation costs				23.5
Other current assets, net				42.5
Income taxes				1.9
Deferred income taxes				22.5
Total Current Assets				679.6
Noncurrent Assets
Property, plant and equipment, net				358.8
Real estate held for entitlement and leasing				81.5
Recoverable from the U.S. government and other third parties for environmental remediation costs				79.3
Deferred income taxes				254.5
Goodwill				164.4
Intangible assets				118.8
Assets held for sale				14.2
Other noncurrent assets, net				76.3
Total Noncurrent Assets				1,217.2
Total Assets				1,896.8
Current Liabilities
Short-term borrowings and current portion of long-term debt, net of deferred financing costs				5.2
Accounts payable				84.5
Reserves for environmental remediation costs				38.3
Postretirement medical and life insurance benefits				6.4
Advance payments on contracts				224.0
Other current liabilities				211.3
Total Current Liabilities				569.7
Noncurrent Liabilities
Senior debt, net of deferred financing costs				91.6
Total senior secured notes				448.2
Convertible subordinated debentures, bearing interest at 4.0625% per annum, interest payments due in June and December, maturing in December 2039				99.4
Other debt, net of deferred financing costs				79.2
Reserves for environmental remediation costs				124.3
Pension benefits				479.1
Postretirement medical and life insurance benefits				50.6
Other noncurrent liabilities				81.1
Total Noncurrent Liabilities				1,453.5
Total Liabilities				2,023.2
Redeemable common stock, par value of $0.10; 0.1 million shares issued and outstanding as of March 31, 2016, December 31, 2015, and November 30, 2015				0.1
Stockholders’ Deficit
Common stock				6.3
Other capital				324.6
Treasury stock				(64.5)
Accumulated deficit				(70.9)
Accumulated other comprehensive loss, net of income taxes				(322.0)
Total Stockholders’ Deficit				(126.5)
Total Liabilities, Redeemable Common Stock and Stockholders’ Deficit				1,896.8
As Reported [Member] | Northrop [Member]
Current Assets
Receivable from Northrop				6.0
Noncurrent Assets
Receivable from Northrop				69.4
Restatement Adjustment [Member]
Current Assets
Cash and cash equivalents				0.0	$ 0.0
Accounts receivable				(16.1)
Inventories				0.1
Recoverable from the U.S. government and other third parties for environmental remediation costs				0.0
Other current assets, net				1.2
Income taxes				0.4
Deferred income taxes				(3.8)
Total Current Assets				(18.2)
Noncurrent Assets
Property, plant and equipment, net				(1.6)
Real estate held for entitlement and leasing				0.0
Recoverable from the U.S. government and other third parties for environmental remediation costs				0.0
Deferred income taxes				1.5
Goodwill				(6.3)
Intangible assets				0.0
Assets held for sale				0.0
Other noncurrent assets, net				8.6
Total Noncurrent Assets				2.2
Total Assets				(16.0)
Current Liabilities
Short-term borrowings and current portion of long-term debt, net of deferred financing costs				0.0
Accounts payable				0.5
Reserves for environmental remediation costs				0.0
Postretirement medical and life insurance benefits				0.0
Advance payments on contracts				(17.0)
Other current liabilities				2.2
Total Current Liabilities				(14.3)
Noncurrent Liabilities
Senior debt, net of deferred financing costs				0.0
Total senior secured notes				0.0
Convertible subordinated debentures, bearing interest at 4.0625% per annum, interest payments due in June and December, maturing in December 2039				0.0
Other debt, net of deferred financing costs				0.0
Reserves for environmental remediation costs				0.0
Pension benefits				0.0
Postretirement medical and life insurance benefits				0.0
Other noncurrent liabilities				0.7
Total Noncurrent Liabilities				0.7
Total Liabilities				(13.6)
Redeemable common stock, par value of $0.10; 0.1 million shares issued and outstanding as of March 31, 2016, December 31, 2015, and November 30, 2015				0.0
Stockholders’ Deficit
Common stock				0.0
Other capital				0.0
Treasury stock				0.0
Accumulated deficit				(3.0)
Accumulated other comprehensive loss, net of income taxes				0.6
Total Stockholders’ Deficit				(2.4)
Total Liabilities, Redeemable Common Stock and Stockholders’ Deficit				(16.0)
Restatement Adjustment [Member] | Northrop [Member]
Current Assets
Receivable from Northrop				0.0
Noncurrent Assets
Receivable from Northrop				$ 0.0