Revisions - Summary of Impact of Errors to Unaudited Condensed Consolidated Cash Flow Statement (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended		9 Months Ended
	May. 31, 2015	Aug. 31, 2014	May. 31, 2014	Feb. 28, 2014	May. 31, 2015	May. 31, 2014	Aug. 31, 2014
Operating Activities
Net income (loss)	$ 18.4	$ (9.9)	$ (50.9)	$ (2.3)	$ 14.5	$ (53.2)	$ (63.1)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Loss from discontinued operations, net of income taxes	0.0	(0.2)	0.8	0.0	(0.2)	0.8	0.6
Depreciation and amortization	16.1	15.8	15.7	14.9	32.1	30.6	46.4
Amortization of financing costs					1.4	1.8	2.7
Stock-based compensation	2.0		1.6		7.3	3.0	4.5
Retirement benefit expense					33.4	17.8	26.7
Loss on debt repurchased	0.5		45.9		0.7	50.8	60.6
Loss on bank amendment	$ 0.0		0.2		0.0	0.2	0.2
Loss on disposal of long-lived assets					0.2	0.0	2.5
Tax benefit on stock-based awards					(1.5)	(1.3)	(1.5)
Changes in assets and liabilities:
Accounts receivable					(0.8)	21.5	(0.8)
Inventories					(11.3)	(25.1)	(25.5)
Other current assets, net					(7.5)	3.7	(3.5)
Income tax receivable					0.0	3.2	0.5
Real estate held for entitlement and leasing					(4.0)	(3.6)	(7.7)
Receivable from Northrop					5.1	(1.2)	(2.0)
Recoverable from the U.S. government and other third parties for environmental remediation costs					0.1	6.6	5.4
Other noncurrent assets					(9.0)	(15.6)	(24.0)
Accounts payable					(15.9)	(28.0)	(7.1)
Postretirement medical and life benefits					(2.6)	(3.2)	(4.2)
Advance payments on contracts					(1.2)	6.1	18.0
Other current liabilities					(25.6)	(27.7)	10.9
Deferred income taxes					(0.9)	(3.6)	(6.1)
Reserves for environmental remediation costs					(4.5)	(7.6)	(2.7)
Other noncurrent liabilities					18.6	1.8	3.4
Net cash provided by (used in) continuing operations					28.4	(22.2)	34.2
Net cash used in discontinued operations					0.0	(0.1)	(0.1)
Net cash (used in) provided by operating activities					$ 28.4	(22.3)	34.1
Previously Reported [Member]
Operating Activities
Net income (loss)		(9.5)	(50.2)	(2.1)		(52.3)	(61.8)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Loss from discontinued operations, net of income taxes		(0.2)	0.8	0.0		0.8	0.6
Depreciation and amortization		$ 15.7	$ 15.4	$ 14.8		30.2	45.9
Amortization of financing costs						1.8	2.7
Stock-based compensation						3.0	4.5
Retirement benefit expense						17.8	26.7
Loss on debt repurchased						50.8	60.6
Loss on bank amendment						0.2	0.2
Loss on disposal of long-lived assets						0.0	2.5
Tax benefit on stock-based awards						(1.3)	(1.5)
Changes in assets and liabilities:
Accounts receivable						22.1	(0.8)
Inventories						(26.8)	(27.2)
Other current assets, net						3.7	(3.5)
Income tax receivable						3.8	1.4
Real estate held for entitlement and leasing						(3.6)	(7.7)
Receivable from Northrop						(1.2)	(2.0)
Recoverable from the U.S. government and other third parties for environmental remediation costs						6.6	5.4
Other noncurrent assets						(15.6)	(24.0)
Accounts payable						(28.0)	(7.1)
Postretirement medical and life benefits						(3.2)	(4.2)
Advance payments on contracts						6.1	18.0
Other current liabilities						(27.7)	10.9
Deferred income taxes						(3.6)	(6.1)
Reserves for environmental remediation costs						(7.6)	(2.7)
Other noncurrent liabilities						1.8	3.4
Net cash provided by (used in) continuing operations						(22.2)	34.2
Net cash used in discontinued operations						(0.1)	(0.1)
Net cash (used in) provided by operating activities						$ (22.3)	$ 34.1