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Component: (Network and Table)
Network
2403412 - Disclosure - Balance Sheet Accounts and Supplemental Disclosures - Accumulated Other Comprehensive Loss, Net of Income Taxes (Details)
(http://gencorp.com/role/BalanceSheetAccountsAndSupplementalDisclosuresAccumulatedOtherComprehensiveLossNetOfIncomeTaxesDetails)
TableAccumulated Other Comprehensive Income (Loss) [Table]
Slicers (applies to each fact value in each table cell)
Reporting Entity [Axis]0000040888 (http://www.sec.gov/CIK)
Accumulated Other Comprehensive Income (Loss) [Line Items]Period [Axis]
2016-01-01 - 2016-12-31
2015-12-01 - 2015-12-31
2014-12-01 - 2015-11-30
Equity Components [Axis]Equity Components [Axis]Equity Components [Axis]
Actuarial Losses, Net [Member]Prior Service Credits, Net [Member]Equity Component [Domain]Actuarial Losses, Net [Member]Prior Service Credits, Net [Member]Equity Component [Domain]Actuarial Losses, Net [Member]Prior Service Credits, Net [Member]Equity Component [Domain]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
 
 
 
 
 
 
 
 
 
Beginning balance
(347,800,000) 
800,000  
(347,000,000) 
(342,600,000) 
900,000  
(341,700,000) 
(337,000,000) 
3,300,000  
(333,700,000) 
Actuarial losses arising during the period, net of income taxes
7,500,000  
0  
7,500,000  
(8,600,000) 
0  
(8,600,000) 
(55,000,000) 
(1,600,000) 
(56,600,000) 
Amortization of actuarial losses and prior service credits, net of income taxes
37,100,000  
(600,000) 
36,500,000  
3,400,000  
(100,000) 
3,300,000  
49,400,000  
(800,000) 
48,600,000  
Ending balance
(303,200,000) 
 
200,000  
 
(303,000,000) 
 
(347,800,000) 
 
800,000  
 
(347,000,000) 
 
(342,600,000) 
 
900,000  
 
(341,700,000)