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Equity - Additional Information (Detail) (USD $)
 0 Months Ended 3 Months Ended 1 Months Ended
Feb. 10, 2015
Mar. 27, 2015
Mar. 28, 2014
Apr. 23, 2015
Dec. 04, 2014
Feb. 05, 2013
Class of Stock [Line Items]            
Aggregate amount of repurchased shares   $ 100,000,000us-gaap_TreasuryStockValueAcquiredCostMethod $ 133,000,000us-gaap_TreasuryStockValueAcquiredCostMethod      
Remaining authorized amount of share repurchase programs   1,445,000,000us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1        
Cash dividend, declared per share $ 0.65us-gaap_CommonStockDividendsPerShareDeclared $ 0.65us-gaap_CommonStockDividendsPerShareDeclared $ 0.60us-gaap_CommonStockDividendsPerShareDeclared      
Cash dividends   58,000,000us-gaap_DividendsCommonStock        
Net reduction of accrued dividends through payment   3,000,000us-gaap_DividendsShareBasedCompensation        
Dividend payable, record date   Mar. 02, 2015        
Dividend payable date   Mar. 16, 2015        
Common Stock [Member]            
Class of Stock [Line Items]            
Number of common shares repurchased   800,000us-gaap_TreasuryStockSharesAcquired
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_CommonStockMember		 1,200,000us-gaap_TreasuryStockSharesAcquired
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_CommonStockMember		      
December 4, 2014 Share Repurchase Program [Member]            
Class of Stock [Line Items]            
Amount of shares authorized to be repurchased         1,500,000,000us-gaap_StockRepurchaseProgramAuthorizedAmount1
/ us-gaap_ShareRepurchaseProgramAxis
= lll_ShareRepurchaseProgramDecemberFourTwoThousandFourteenMember		  
December 4, 2014 Share Repurchase Program [Member] | Subsequent Event [Member]            
Class of Stock [Line Items]            
Average price per share of repurchased shares       $ 125.19us-gaap_TreasuryStockAcquiredAverageCostPerShare
/ us-gaap_ShareRepurchaseProgramAxis
= lll_ShareRepurchaseProgramDecemberFourTwoThousandFourteenMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember		    
Aggregate amount of repurchased shares       36,000,000us-gaap_TreasuryStockValueAcquiredCostMethod
/ us-gaap_ShareRepurchaseProgramAxis
= lll_ShareRepurchaseProgramDecemberFourTwoThousandFourteenMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember		    
December 4, 2014 Share Repurchase Program [Member] | Common Stock [Member] | Subsequent Event [Member]            
Class of Stock [Line Items]            
Number of common shares repurchased       287,303us-gaap_TreasuryStockSharesAcquired
/ us-gaap_ShareRepurchaseProgramAxis
= lll_ShareRepurchaseProgramDecemberFourTwoThousandFourteenMember
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_CommonStockMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember		    
February 5, 2013 Share Repurchase Program [Member]            
Class of Stock [Line Items]            
Amount of shares authorized to be repurchased           1,500,000,000us-gaap_StockRepurchaseProgramAuthorizedAmount1
/ us-gaap_ShareRepurchaseProgramAxis
= lll_ShareRepurchaseProgramFebruaryFiveTwoThousandThirteenMember
Average price per share of repurchased shares   $ 127.36us-gaap_TreasuryStockAcquiredAverageCostPerShare
/ us-gaap_ShareRepurchaseProgramAxis
= lll_ShareRepurchaseProgramFebruaryFiveTwoThousandThirteenMember		        
Aggregate amount of repurchased shares   $ 100,000,000us-gaap_TreasuryStockValueAcquiredCostMethod
/ us-gaap_ShareRepurchaseProgramAxis
= lll_ShareRepurchaseProgramFebruaryFiveTwoThousandThirteenMember		        
February 5, 2013 Share Repurchase Program [Member] | Common Stock [Member]            
Class of Stock [Line Items]            
Number of common shares repurchased   788,189us-gaap_TreasuryStockSharesAcquired
/ us-gaap_ShareRepurchaseProgramAxis
= lll_ShareRepurchaseProgramFebruaryFiveTwoThousandThirteenMember
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_CommonStockMember