Condensed Consolidating Financial Information - Schedule of Unaudited Condensed Consolidating Balance Sheets (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015	Nov. 30, 2015	Feb. 28, 2015	Nov. 30, 2014
Condensed Balance Sheet Statements, Captions [Line Items]
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, Northrop, and other third parties for environmental remediation costs	33.1	30.0	30.0
Other current assets, net		69.2	61.5
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
Property, plant and equipment, net	359.4	363.3	365.8	357.2
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
Intercompany receivable	0.0	0.0	0.0
Investments in subsidiaries	0.0	0.0	0.0
Other noncurrent assets and intangibles, net	333.4	338.7	339.7
Total Assets	1,988.0	2,025.5	2,023.3	1,880.8
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
Other current liabilities and advance payments on contracts	381.3	434.0	405.0
Postretirement medical and life insurance benefits	6.0	6.0	6.0	6.4
Total Current Liabilities	516.3	542.1	554.1	555.4
Long-term debt, net	620.4	633.7	635.1
Reserves for environmental remediation costs	262.2	269.7	273.5	124.3
Pension benefits	575.0	580.6	566.2	479.1
Intercompany payable	0.0	0.0	0.0
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 Liabilities	$ 2,112.0	$ 2,166.1	$ 2,168.8	2,009.6
Commitments and contingencies
Redeemable common stock	$ 1.3	$ 1.6	$ 0.9
Total stockholders’ (deficit) equity	(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
Eliminations [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	(0.2)	(6.7)	(10.8)	(0.7)	(5.7)
Accounts receivable	0.0	0.0	0.0
Inventories	0.0	0.0	0.0
Recoverable from the U.S. government, Northrop, and other third parties for environmental remediation costs	0.0	0.0	0.0
Other current assets, net		0.0	0.0
Other current assets, net	0.0
Income taxes			(41.6)
Deferred income taxes	0.0	0.0	0.0
Total Current Assets	(0.2)	(6.7)	(52.4)
Property, plant and equipment, net	0.0	0.0	0.0
Recoverable from the U.S. government and other third parties for environmental remediation costs	0.0	0.0	0.0
Deferred income taxes	0.0	0.0	0.0
Goodwill	0.0	0.0	0.0
Intercompany receivable	(139.4)	(169.3)	(227.4)
Investments in subsidiaries	(573.8)	(550.6)	(543.2)
Other noncurrent assets and intangibles, net	0.0	0.0	0.0
Total Assets	(713.4)	(726.6)	(823.0)
Short-term borrowings and current portion of long-term debt, net of deferred financing costs	0.0	0.0	0.0
Accounts payable	(0.2)	(6.7)	(10.8)
Reserves for environmental remediation costs	0.0	0.0	0.0
Other current liabilities and advance payments on contracts	0.0	0.0	(41.6)
Postretirement medical and life insurance benefits	0.0	0.0	0.0
Total Current Liabilities	(0.2)	(6.7)	(52.4)
Long-term debt, net	0.0	0.0	0.0
Reserves for environmental remediation costs	0.0	0.0	0.0
Pension benefits	0.0	0.0	0.0
Intercompany payable	(139.4)	(169.3)	(227.4)
Postretirement medical and life insurance benefits	0.0	0.0	0.0
Other noncurrent liabilities	0.0	0.0	0.0
Total Liabilities	$ (139.6)	$ (176.0)	(279.8)
Commitments and contingencies
Redeemable common stock	$ 0.0	$ 0.0	0.0
Total stockholders’ (deficit) equity	(573.8)	(550.6)	(543.2)
Total Liabilities, Redeemable Common Stock and Stockholders’ Deficit	(713.4)	(726.6)	(823.0)
Parent [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	155.4	215.2	221.9	215.9	271.6
Accounts receivable	0.0	0.0	0.0
Inventories	0.0	0.0	0.0
Recoverable from the U.S. government, Northrop, and other third parties for environmental remediation costs	0.0	0.0	0.0
Other current assets, net		4.2	3.1
Other current assets, net	4.2
Income taxes			44.2
Deferred income taxes	5.5	5.5	6.5
Total Current Assets	165.1	224.9	275.7
Property, plant and equipment, net	4.8	4.7	4.7
Recoverable from the U.S. government and other third parties for environmental remediation costs	0.7	0.7	0.7
Deferred income taxes	68.4	66.5	66.2
Goodwill	0.0	0.0	0.0
Intercompany receivable	0.0	0.0	0.0
Investments in subsidiaries	573.8	550.6	543.2
Other noncurrent assets and intangibles, net	19.1	19.3	19.8
Total Assets	831.9	866.7	910.3
Short-term borrowings and current portion of long-term debt, net of deferred financing costs	5.0	5.0	5.0
Accounts payable	0.8	1.1	1.0
Reserves for environmental remediation costs	0.7	0.7	0.7
Other current liabilities and advance payments on contracts	23.4	30.5	26.8
Postretirement medical and life insurance benefits	4.6	4.6	4.6
Total Current Liabilities	34.5	41.9	38.1
Long-term debt, net	620.4	633.7	635.0
Reserves for environmental remediation costs	3.7	4.4	4.5
Pension benefits	107.4	106.8	98.8
Intercompany payable	139.4	169.3	227.4
Postretirement medical and life insurance benefits	31.8	32.4	32.9
Other noncurrent liabilities	18.7	18.8	19.1
Total Liabilities	$ 955.9	$ 1,007.3	1,055.8
Commitments and contingencies
Redeemable common stock	$ 1.3	$ 1.6	0.9
Total stockholders’ (deficit) equity	(125.3)	(142.2)	(146.4)
Total Liabilities, Redeemable Common Stock and Stockholders’ Deficit	831.9	866.7	910.3
Guarantor Subsidiaries [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	0.0	0.0	0.0	0.0	0.0
Accounts receivable	179.0	166.2	167.4
Inventories	164.6	148.4	150.8
Recoverable from the U.S. government, Northrop, and other third parties for environmental remediation costs	33.1	30.0	30.0
Other current assets, net		64.2	57.5
Other current assets, net	65.7
Income taxes			0.3
Deferred income taxes	30.1	29.8	20.4
Total Current Assets	472.5	438.6	426.4
Property, plant and equipment, net	349.0	352.8	355.3
Recoverable from the U.S. government and other third parties for environmental remediation costs	201.2	206.5	209.7
Deferred income taxes	200.6	204.7	203.4
Goodwill	158.1	158.1	158.1
Intercompany receivable	106.0	138.4	192.9
Investments in subsidiaries	0.0	0.0	0.0
Other noncurrent assets and intangibles, net	251.7	257.9	258.6
Total Assets	1,739.1	1,757.0	1,804.4
Short-term borrowings and current portion of long-term debt, net of deferred financing costs	0.2	0.3	0.3
Accounts payable	83.6	67.6	112.9
Reserves for environmental remediation costs	36.4	31.9	31.9
Other current liabilities and advance payments on contracts	354.0	400.3	413.4
Postretirement medical and life insurance benefits	1.4	1.4	1.4
Total Current Liabilities	475.6	501.5	559.9
Long-term debt, net	0.0	0.0	0.1
Reserves for environmental remediation costs	258.5	265.3	269.0
Pension benefits	467.6	473.8	467.4
Intercompany payable	0.0	0.0	0.0
Postretirement medical and life insurance benefits	12.3	12.4	12.6
Other noncurrent liabilities	62.8	64.0	62.6
Total Liabilities	$ 1,276.8	$ 1,317.0	1,371.6
Commitments and contingencies
Redeemable common stock	$ 0.0	$ 0.0	0.0
Total stockholders’ (deficit) equity	462.3	440.0	432.8
Total Liabilities, Redeemable Common Stock and Stockholders’ Deficit	1,739.1	1,757.0	1,804.4
Non-guarantor Subsidiaries [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	0.3	0.0	0.0	$ 0.5	$ 0.0
Accounts receivable	3.3	3.3	4.1
Inventories	6.0	7.8	6.7
Recoverable from the U.S. government, Northrop, and other third parties for environmental remediation costs	0.0	0.0	0.0
Other current assets, net		0.8	0.9
Other current assets, net	0.9
Income taxes			0.0
Deferred income taxes	1.1	1.2	1.2
Total Current Assets	11.6	13.1	12.9
Property, plant and equipment, net	5.6	5.8	5.8
Recoverable from the U.S. government and other third parties for environmental remediation costs	0.0	0.0	0.0
Deferred income taxes	17.2	17.1	17.1
Goodwill	0.0	0.0	0.0
Intercompany receivable	33.4	30.9	34.5
Investments in subsidiaries	0.0	0.0	0.0
Other noncurrent assets and intangibles, net	62.6	61.5	61.3
Total Assets	130.4	128.4	131.6
Short-term borrowings and current portion of long-term debt, net of deferred financing costs	0.0	0.0	0.0
Accounts payable	2.5	2.2	2.1
Reserves for environmental remediation costs	0.0	0.0	0.0
Other current liabilities and advance payments on contracts	3.9	3.2	6.4
Postretirement medical and life insurance benefits	0.0	0.0	0.0
Total Current Liabilities	6.4	5.4	8.5
Long-term debt, net	0.0	0.0	0.0
Reserves for environmental remediation costs	0.0	0.0	0.0
Pension benefits	0.0	0.0	0.0
Intercompany payable	0.0	0.0	0.0
Postretirement medical and life insurance benefits	0.0	0.0	0.0
Other noncurrent liabilities	12.5	12.4	12.7
Total Liabilities	$ 18.9	$ 17.8	21.2
Commitments and contingencies
Redeemable common stock	$ 0.0	$ 0.0	0.0
Total stockholders’ (deficit) equity	111.5	110.6	110.4
Total Liabilities, Redeemable Common Stock and Stockholders’ Deficit	$ 130.4	$ 128.4	$ 131.6