Restatement - Schedule of Effects of Prior Period Errors on the Consolidated Financial Statements - Consolidated Statements of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended								6 Months Ended		9 Months Ended		12 Months Ended
	Nov. 30, 2015	Aug. 31, 2015	May. 31, 2015	Feb. 28, 2015	Nov. 30, 2014	Aug. 31, 2014	May. 31, 2014	Feb. 28, 2014	May. 31, 2015	May. 31, 2014	Aug. 31, 2015	Aug. 31, 2014	Nov. 30, 2015	Nov. 30, 2014	Nov. 30, 2013
Operating Activities
Net (loss) income	$ 7.7	$ (37.9)	$ 17.3	$ (3.3)	$ 11.9	$ (10.5)	$ (49.2)	$ (2.2)	$ 14.0	$ (51.4)	$ (23.9)	$ (61.9)	$ (16.2)	$ (50.0)	$ 162.9
Adjustments to reconcile net (loss) income to net cash provided by operating activities:
(Income) loss from discontinued operations, net of income taxes	(0.1)	(0.6)	0.0	(0.2)	0.1	(0.2)	0.8	0.0	(0.2)	0.8	(0.8)	0.6	(0.9)	0.7	(0.2)
Depreciation and amortization		16.1	16.1	16.3	17.3	15.7	15.8	14.9	32.4	30.7	48.5	46.4	65.1	63.7	43.5
Amortization of financing costs				0.7				0.9	1.4	1.8	2.0	2.7	2.7	3.6	4.5
Stock-based compensation				5.3				1.4	8.3	3.0	10.4	4.5	8.6	5.7	14.1
Retirement benefit expense				16.8				9.1	33.8	18.3	50.6	27.5	67.6	36.5	65.0
Loss on debt repurchased		1.1	0.5	0.2	0.0	9.8	45.9	4.9	0.7	50.8	1.8	60.6	1.9	60.6	5.0
Loss on bank amendment				0.0				0.0		0.2		0.2	0.0	0.2	0.0
Loss on disposal of long-lived assets				0.2					0.2		0.2	2.5	0.7	2.8	0.0
Gain on sale of technology													(1.0)	(6.8)	0.0
Tax benefit on stock-based awards				(1.4)				(1.1)	(1.5)	(1.3)	(2.0)	(1.3)	(2.5)	(1.3)	(0.2)
Changes in assets and liabilities, net of effects from acquisition:
Accounts receivable				(19.5)				13.6	(5.1)	22.1	(18.8)	(1.1)	(1.0)	28.9	(24.0)
Inventories				(23.5)				(29.4)	(12.1)	(25.7)	(9.9)	(25.8)	(19.5)	(32.0)	(26.4)
Other current assets, net				(5.3)				(1.5)	(8.4)	3.5	(20.1)	(2.2)	(22.8)	(10.8)	(4.4)
Income tax receivable								0.0		1.9			(2.9)	3.7	(11.8)
Real estate held for entitlement and leasing				(1.5)				(1.1)	(4.0)	(3.6)	(5.1)	(7.7)	(7.8)	(15.0)	(4.4)
Receivable from Northrop				(0.6)				(0.3)	(0.9)	(1.2)	(1.2)	(2.0)	6.1	(2.8)	3.3
Recoverable from the U.S. government and other third parties for environmental remediation costs				3.8				0.2	6.1	6.6	(39.8)	5.4	(127.8)	8.5	15.1
Other noncurrent assets				13.4				(6.8)	(8.7)	(15.5)	(10.8)	(24.4)	11.9	(24.1)	(2.0)
Assets held for sale				(14.2)								0.0
Accounts payable				(19.0)				(25.1)	(15.9)	(27.6)	(15.3)	(6.7)	(5.1)	(18.2)	49.7
Retirement benefits				(1.6)				(1.5)	(2.6)	(3.2)	(3.7)	(4.2)	(4.9)	(5.3)	(5.4)
Advance payments on contracts				9.6				(6.3)	(0.1)	2.9	14.3	15.5	6.3	96.9	(47.8)
Other current liabilities				(7.9)				10.9	(22.0)	(25.0)	19.5	10.6	(17.8)	19.8	57.8
Deferred income taxes				(1.1)				(5.0)	(0.6)	(3.9)	(10.7)	(3.4)	(27.6)	(7.1)	(199.5)
Reserves for environmental remediation costs				(3.4)				(0.9)	(4.5)	(7.6)	70.1	(2.7)	140.1	(5.3)	(18.2)
Other noncurrent liabilities and other				0.6				0.0	18.1	1.2	15.2	1.3	12.0	(0.2)	0.9
Net cash provided by continuing operations				(35.6)				(25.3)		(22.2)		34.4	65.2	152.7	77.5
Net cash used in discontinued operations				0.0				0.0		(0.1)		(0.1)	(0.1)	(2.1)	(0.1)
Net Cash Provided by Operating Activities				(35.6)				(25.3)	28.4	(22.3)	70.5	34.3	65.1	150.6	77.4
Investing Activities
Purchases of restricted cash investments													0.0	0.0	(470.0)
Sale of restricted cash investments													0.0	0.0	470.0
Purchase of Rocketdyne Business				0.0								0.2	0.0	0.2	(411.2)
Purchases of investments													0.0	0.0	(0.5)
Proceeds from sale of technology													1.0	7.5	0.0
Capital expenditures				(4.3)				(9.3)	(9.4)	(18.5)	(17.9)	(31.9)	(36.8)	(43.4)	(63.2)
Net cash provided by (used in) investing activities				(4.3)				(9.3)	(9.4)	(18.5)	(17.9)	(31.7)	(35.8)	(35.7)	(474.9)
Financing Activities
Proceeds from issuance of debt				0.0				0.0		179.0		189.0	0.0	189.0	460.0
Debt issuance costs				0.0				0.0		(4.1)		(4.2)	0.0	(4.2)	(14.9)
Debt repayments/repurchases				(9.3)				(10.0)	(28.5)	(145.8)	(72.0)	(165.0)	(81.2)	(166.3)	(12.8)
Proceeds from shares issued under equity plans, net									0.0		1.3		1.3	0.2	0.7
Repurchase of shares to satisfy tax withholding obligations				(2.4)				(1.4)	(4.4)	(2.0)	(6.5)	(1.9)	(6.7)	(2.1)	(0.2)
Purchase of treasury stock				0.0				(8.6)		(64.5)		(64.5)	0.0	(64.5)	0.0
Tax benefit on stock-based awards				1.4				1.1	1.5	1.3	2.0	1.3	2.5	1.3	0.2
Net Cash (Used in) Provided by Financing Activities				(10.3)				(18.9)	(31.4)	(36.1)	(75.2)	(45.3)	(84.1)	(46.6)	433.0
Net (Decrease) Increase in Cash and Cash Equivalents				(50.2)				(53.5)	(12.4)	(76.9)	(22.6)	(42.7)	(54.8)	68.3	35.5
Cash and Cash Equivalents at Beginning of Period	243.3	253.5	215.7	265.9	154.9	120.7	144.1	197.6	265.9	197.6	265.9	197.6	265.9	197.6	162.1
Cash and Cash Equivalents at End of Period	211.1	243.3	253.5	215.7	265.9	154.9	120.7	144.1	253.5	120.7	243.3	154.9	211.1	265.9	197.6
As Reported [Member]
Operating Activities
Net (loss) income		(38.1)	18.4	(3.9)	10.1	(9.9)	(50.9)	(2.3)	14.5	(53.2)	(23.6)	(63.1)		(53.0)	167.9
Adjustments to reconcile net (loss) income to net cash provided by operating activities:
(Income) loss from discontinued operations, net of income taxes		(0.6)	0.0	(0.2)	0.1	(0.2)	0.8	0.0	(0.2)	0.8	(0.8)	0.6		0.7	(0.2)
Depreciation and amortization		16.1	16.1	16.0	17.3	15.8	15.7	14.9	32.1	30.6	48.2	46.4		63.7	43.8
Amortization of financing costs				0.7				0.9	1.4	1.8	2.0	2.7		3.6	4.5
Stock-based compensation				5.3				1.4	7.3	3.0	9.6	4.5		5.7	14.1
Retirement benefit expense				16.6				8.9	33.4	17.8	50.0	26.7		35.6	65.0
Loss on debt repurchased		1.1	0.5	0.2	0.0	9.8	45.9	4.9	0.7	50.8	1.8	60.6		60.6	5.0
Loss on bank amendment				0.0				0.0		0.2		0.2		0.2
Loss on disposal of long-lived assets				0.2					0.2		0.2	2.5		2.8
Gain on sale of technology														(6.8)
Tax benefit on stock-based awards				(1.4)				(1.1)	(1.5)	(1.3)	(2.0)	(1.5)		(1.5)	0.0
Changes in assets and liabilities, net of effects from acquisition:
Accounts receivable				(33.2)				14.3	(0.8)	21.5	(13.8)	(0.8)		41.0	(37.6)
Inventories				(22.4)				(31.6)	(11.3)	(25.1)	(9.7)	(25.5)		(33.9)	(25.5)
Other current assets, net				(6.2)				0.0	(7.5)	3.7	(19.4)	(3.0)		(12.8)	0.1
Income tax receivable								6.6		3.2				11.1	(12.6)
Real estate held for entitlement and leasing				(1.5)				(1.1)	(4.0)	(3.6)	(5.1)	(7.7)		(15.0)	(4.4)
Receivable from Northrop				5.4				(0.3)	5.1	(1.2)	4.8	(2.0)		(2.8)	(2.7)
Recoverable from the U.S. government and other third parties for environmental remediation costs				(2.2)				0.2	0.1	6.6	(45.8)	5.4		8.5	21.1
Other noncurrent assets				14.3				(4.2)	(9.0)	(15.6)	(11.2)	(24.0)		(24.3)	(7.8)
Assets held for sale				(14.2)								0.0
Accounts payable				(19.0)				(24.5)	(15.9)	(28.0)	(14.8)	(7.1)		(19.0)	50.1
Retirement benefits				(1.6)				(1.5)	(2.6)	(3.2)	(3.7)	(4.2)		(5.3)	(5.4)
Advance payments on contracts				25.5				(9.2)	(1.2)	6.1	13.2	18.0		94.1	(43.9)
Other current liabilities				(11.3)				6.4	(25.6)	(27.7)	15.7	10.9		22.0	56.8
Deferred income taxes				(0.3)				(6.8)	(0.9)	(3.6)	(11.8)	(6.1)		(18.1)	(191.3)
Reserves for environmental remediation costs				(3.4)				(0.9)	(4.5)	(7.6)	70.1	(2.7)		(5.3)	(18.2)
Other noncurrent liabilities and other				1.0				(0.3)	18.6	1.8	16.6	3.4		0.7	(1.1)
Net cash provided by continuing operations				(35.6)				(25.3)		(22.2)		34.2		152.5	77.7
Net cash used in discontinued operations				0.0				0.0		(0.1)		(0.1)		(2.1)	(0.1)
Net Cash Provided by Operating Activities				(35.6)				(25.3)	28.4	(22.3)	70.5	34.1		150.4	77.6
Investing Activities
Purchases of restricted cash investments															(470.0)
Sale of restricted cash investments															470.0
Purchase of Rocketdyne Business				0.0								0.2		0.2	(411.2)
Purchases of investments															(0.5)
Proceeds from sale of technology														7.5
Capital expenditures				(4.3)				(9.3)	(9.4)	(18.5)	(17.9)	(31.9)		(43.4)	(63.2)
Net cash provided by (used in) investing activities				(4.3)				(9.3)	(9.4)	(18.5)	(17.9)	(31.7)		(35.7)	(474.9)
Financing Activities
Proceeds from issuance of debt				0.0				0.0		179.0		189.0		189.0	460.0
Debt issuance costs				0.0				0.0		(4.1)		(4.2)		(4.2)	(14.9)
Debt repayments/repurchases				(9.3)				(10.0)	(28.5)	(145.8)	(72.0)	(165.0)		(166.3)	(12.8)
Proceeds from shares issued under equity plans, net									0.0		1.3			0.2	0.7
Repurchase of shares to satisfy tax withholding obligations				(2.4)				(1.4)	(4.4)	(2.0)	(6.5)	(1.9)		(2.1)	(0.2)
Purchase of treasury stock				0.0				(8.6)		(64.5)		(64.5)		(64.5)
Tax benefit on stock-based awards				1.4				1.1	1.5	1.3	2.0	1.5		1.5	0.0
Net Cash (Used in) Provided by Financing Activities				(10.3)				(18.9)	(31.4)	(36.1)	(75.2)	(45.1)		(46.4)	432.8
Net (Decrease) Increase in Cash and Cash Equivalents				(50.2)				(53.5)	(12.4)	(76.9)	(22.6)	(42.7)		68.3	35.5
Cash and Cash Equivalents at Beginning of Period	243.3	253.5	215.7	265.9	154.9	120.7	144.1	197.6	265.9	197.6	265.9	197.6	265.9	197.6	162.1
Cash and Cash Equivalents at End of Period		243.3	253.5	215.7	265.9	154.9	120.7	144.1	253.5	120.7	243.3	154.9		265.9	197.6
Adjustments [Member]
Operating Activities
Net (loss) income		0.2	(1.1)	0.6	1.8	(0.6)	1.7	0.1	(0.5)	1.8	(0.3)	1.2		3.0	(5.0)
Adjustments to reconcile net (loss) income to net cash provided by operating activities:
(Income) loss from discontinued operations, net of income taxes		0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0		0.0	0.0
Depreciation and amortization		0.0	0.0	0.3	0.0	(0.1)	0.1	0.0	0.3	0.1	0.3	0.0		0.0	(0.3)
Amortization of financing costs				0.0				0.0	0.0	0.0	0.0	0.0		0.0	0.0
Stock-based compensation				0.0				0.0	1.0	0.0	0.8	0.0		0.0	0.0
Retirement benefit expense				0.2				0.2	0.4	0.5	0.6	0.8		0.9	0.0
Loss on debt repurchased		0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0		0.0	0.0
Loss on bank amendment				0.0				0.0		0.0		0.0		0.0
Loss on disposal of long-lived assets				0.0					0.0		0.0	0.0		0.0
Gain on sale of technology														0.0
Tax benefit on stock-based awards				0.0				0.0	0.0	0.0	0.0	0.2		0.2	(0.2)
Changes in assets and liabilities, net of effects from acquisition:
Accounts receivable				13.7				(0.7)	(4.3)	0.6	(5.0)	(0.3)		(12.1)	13.6
Inventories				(1.1)				2.2	(0.8)	(0.6)	(0.2)	(0.3)		1.9	(0.9)
Other current assets, net				0.9				(1.5)	(0.9)	(0.2)	(0.7)	0.8		2.0	(4.5)
Income tax receivable								(6.6)		(1.3)				(7.4)	0.8
Real estate held for entitlement and leasing				0.0				0.0	0.0	0.0	0.0	0.0		0.0	0.0
Receivable from Northrop				(6.0)				0.0	(6.0)	0.0	(6.0)	0.0		0.0	6.0
Recoverable from the U.S. government and other third parties for environmental remediation costs				6.0				0.0	6.0	0.0	6.0	0.0		0.0	(6.0)
Other noncurrent assets				(0.9)				(2.6)	0.3	0.1	0.4	(0.4)		0.2	5.8
Assets held for sale				0.0								0.0
Accounts payable				0.0				(0.6)	0.0	0.4	(0.5)	0.4		0.8	(0.4)
Retirement benefits				0.0				0.0	0.0	0.0	0.0	0.0		0.0	0.0
Advance payments on contracts				(15.9)				2.9	1.1	(3.2)	1.1	(2.5)		2.8	(3.9)
Other current liabilities				3.4				4.5	3.6	2.7	3.8	(0.3)		(2.2)	1.0
Deferred income taxes				(0.8)				1.8	0.3	(0.3)	1.1	2.7		11.0	(8.2)
Reserves for environmental remediation costs				0.0				0.0	0.0	0.0	0.0	0.0		0.0	0.0
Other noncurrent liabilities and other				(0.4)				0.3	(0.5)	(0.6)	(1.4)	(2.1)		(0.9)	2.0
Net cash provided by continuing operations				0.0				0.0		0.0		0.2		0.2	(0.2)
Net cash used in discontinued operations				0.0				0.0		0.0		0.0		0.0	0.0
Net Cash Provided by Operating Activities				0.0				0.0	0.0	0.0	0.0	0.2		0.2	(0.2)
Investing Activities
Purchases of restricted cash investments															0.0
Sale of restricted cash investments															0.0
Purchase of Rocketdyne Business				0.0								0.0		0.0	0.0
Purchases of investments															0.0
Proceeds from sale of technology														0.0
Capital expenditures				0.0				0.0	0.0	0.0	0.0	0.0		0.0	0.0
Net cash provided by (used in) investing activities				0.0				0.0	0.0	0.0	0.0	0.0		0.0	0.0
Financing Activities
Proceeds from issuance of debt				0.0				0.0		0.0		0.0		0.0	0.0
Debt issuance costs				0.0				0.0		0.0		0.0		0.0	0.0
Debt repayments/repurchases				0.0				0.0	0.0	0.0	0.0	0.0		0.0	0.0
Proceeds from shares issued under equity plans, net									0.0		0.0			0.0	0.0
Repurchase of shares to satisfy tax withholding obligations				0.0				0.0	0.0	0.0	0.0	0.0		0.0	0.0
Purchase of treasury stock				0.0				0.0		0.0		0.0		0.0
Tax benefit on stock-based awards				0.0				0.0	0.0	0.0	0.0	(0.2)		(0.2)	0.2
Net Cash (Used in) Provided by Financing Activities				0.0				0.0	0.0	0.0	0.0	(0.2)		(0.2)	0.2
Net (Decrease) Increase in Cash and Cash Equivalents				0.0				0.0	0.0	0.0	0.0	0.0		0.0	0.0
Cash and Cash Equivalents at Beginning of Period	$ 0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	$ 0.0	0.0	0.0
Cash and Cash Equivalents at End of Period		$ 0.0	$ 0.0	$ 0.0	$ 0.0	$ 0.0	$ 0.0	$ 0.0	$ 0.0	$ 0.0	$ 0.0	$ 0.0		$ 0.0	$ 0.0