Restatement - Schedule of Effects of Prior Period Errors on the Consolidated Financial Statements - Consolidated Statements of Cash Flows (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended	12 Months Ended
	Dec. 31, 2015	Mar. 31, 2016	Feb. 28, 2015	Aug. 31, 2015	Nov. 30, 2014	Nov. 30, 2013
Operating Activities
Net income (loss)	$ 7.0	$ 5.1	$ (3.3)
Adjustments to reconcile net income (loss) to net cash used in operating activities:
Loss (income) from discontinued operations, net of income taxes	0.0	0.1	(0.2)
Depreciation and amortization	5.1	15.1	16.3
Amortization of financing costs	0.2	0.6	0.7
Stock-based compensation	(0.4)	2.3	5.3
Retirement benefit expense	5.6	17.2	16.8
Loss on debt repurchased	0.0	0.3	0.2
Loss on disposal of long-lived assets	0.0	0.0	0.2
Tax benefit on stock-based awards	(2.4)	0.0	(1.4)
Changes in assets and liabilities:
Accounts receivable	2.0	(12.8)	(19.5)
Inventories	1.3	(14.4)	(23.5)
Other current assets, net			(5.3)
Real estate held for entitlement and leasing	(0.1)	(1.2)	(1.5)
Receivable from Northrop	(0.5)	0.5	(0.6)
Recoverable from the U.S. government and other third parties for environmental remediation costs	3.2	2.2	3.8
Other noncurrent assets	0.5	2.8	13.4
Assets held for sale	0.0	0.0	(14.2)
Accounts payable	(41.0)	22.5	(19.0)
Pension and postretirement medical and life benefits	(0.2)	(8.7)	(1.6)
Advance payments on contracts	27.2	(30.1)	9.6
Other current liabilities	5.6	(23.3)	(7.9)
Deferred income taxes	(7.1)	(3.8)	(1.1)
Reserves for environmental remediation costs	(3.8)	(3.0)	(3.4)
Other noncurrent liabilities	0.3	(1.5)	0.6
Net cash provided by (used in) continuing operations			(35.6)
Net cash used in discontinued operations			0.0
Net cash (used in) provided by operating activities	(2.3)	(31.7)	(35.6)
Investing Activities
Capital expenditures	(1.2)	(7.7)	(4.3)
Net cash used in investing activities	(1.2)	(7.7)	(4.3)
Financing Activities
Debt repayments	(1.3)	(14.4)	(9.3)
Repurchase of shares to satisfy employee tax withholding obligations	(0.2)	(0.7)	(2.4)
Tax benefit on stock-based awards	2.4	0.0	1.4
Net Cash (Used in) Provided by Financing Activities			(10.3)
Net (decrease) increase in cash and cash equivalents	(2.6)	(53.0)	(50.2)
Cash and Cash Equivalents at Beginning of Period	211.1	208.5	265.9	$ 265.9
Cash and Cash Equivalents at End of Period	$ 208.5	$ 155.5	215.7		$ 265.9
As Reported [Member]
Operating Activities
Net income (loss)			(3.9)
Adjustments to reconcile net income (loss) to net cash used in operating activities:
Loss (income) from discontinued operations, net of income taxes			(0.2)
Depreciation and amortization			16.0
Amortization of financing costs			0.7
Stock-based compensation			5.3
Retirement benefit expense			16.6
Loss on debt repurchased			0.2
Loss on disposal of long-lived assets			0.2
Tax benefit on stock-based awards			(1.4)
Changes in assets and liabilities:
Accounts receivable			(33.2)
Inventories			(22.4)
Other current assets, net			(6.2)
Real estate held for entitlement and leasing			(1.5)
Receivable from Northrop			5.4
Recoverable from the U.S. government and other third parties for environmental remediation costs			(2.2)
Other noncurrent assets			14.3
Assets held for sale			(14.2)
Accounts payable			(19.0)
Pension and postretirement medical and life benefits			(1.6)
Advance payments on contracts			25.5
Other current liabilities			(11.3)
Deferred income taxes			(0.3)
Reserves for environmental remediation costs			(3.4)
Other noncurrent liabilities			1.0
Net cash provided by (used in) continuing operations			(35.6)
Net cash used in discontinued operations			0.0
Net cash (used in) provided by operating activities			(35.6)
Investing Activities
Capital expenditures			(4.3)
Net cash used in investing activities			(4.3)
Financing Activities
Debt repayments			(9.3)
Repurchase of shares to satisfy employee tax withholding obligations			(2.4)
Tax benefit on stock-based awards			1.4
Net Cash (Used in) Provided by Financing Activities			(10.3)
Net (decrease) increase in cash and cash equivalents			(50.2)
Cash and Cash Equivalents at Beginning of Period			265.9	265.9
Cash and Cash Equivalents at End of Period			215.7		265.9
Restatement Adjustment [Member]
Operating Activities
Net income (loss)			0.6	(0.3)	3.0	$ (5.0)
Adjustments to reconcile net income (loss) to net cash used in operating activities:
Loss (income) from discontinued operations, net of income taxes			0.0
Depreciation and amortization			0.3
Amortization of financing costs			0.0
Stock-based compensation			0.0
Retirement benefit expense			0.2
Loss on debt repurchased			0.0
Loss on disposal of long-lived assets			0.0
Tax benefit on stock-based awards			0.0
Changes in assets and liabilities:
Accounts receivable			13.7
Inventories			(1.1)
Other current assets, net			0.9
Real estate held for entitlement and leasing			0.0
Receivable from Northrop			(6.0)
Recoverable from the U.S. government and other third parties for environmental remediation costs			6.0
Other noncurrent assets			(0.9)
Assets held for sale			0.0
Accounts payable			0.0
Pension and postretirement medical and life benefits			0.0
Advance payments on contracts			(15.9)
Other current liabilities			3.4
Deferred income taxes			(0.8)
Reserves for environmental remediation costs			0.0
Other noncurrent liabilities			(0.4)
Net cash provided by (used in) continuing operations			0.0
Net cash used in discontinued operations			0.0
Net cash (used in) provided by operating activities			0.0
Investing Activities
Capital expenditures			0.0
Net cash used in investing activities			0.0
Financing Activities
Debt repayments			0.0
Repurchase of shares to satisfy employee tax withholding obligations			0.0
Tax benefit on stock-based awards			0.0
Net Cash (Used in) Provided by Financing Activities			0.0
Net (decrease) increase in cash and cash equivalents			0.0
Cash and Cash Equivalents at Beginning of Period			0.0	$ 0.0
Cash and Cash Equivalents at End of Period			$ 0.0		$ 0.0