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Stock-Based Compensation Plans - Additional Information (Detail) (USD $)
In Millions, except Share data, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Aggregate number of shares to be issued 21,250,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized  
Number of shares available for future grants 1,262,031us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant  
Stock-based compensation expense recognized $ 11us-gaap_AllocatedShareBasedCompensationExpense $ 9us-gaap_AllocatedShareBasedCompensationExpense
Unrecognized compensation costs related to non-vested stocks $ 62us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized  
Weighted average period for recognizing non-vested stock based compensation costs 1 year 2 months  
Stock Options    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Share-based compensation plans, award vesting period 3 years  
Shares - Stock Options 1,067,190us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
Share-based compensation plans, award term 10 years  
Restricted Stock Units    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Share-based compensation plans, award vesting period   3 years
Shares - Other than Stock Options 765,750us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
Total Shareholder Return (TSR) Performance Awards    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Share-based compensation plans, award vesting period 3 years  
Shares - Other than Stock Options 273,560us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= x_TotalStockholdersReturnTSRPerformanceBasedRestrictedStockMember
279,570us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= x_TotalStockholdersReturnTSRPerformanceBasedRestrictedStockMember
Total Shareholder Return (TSR) Performance Awards | Minimum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Vesting of performance awards as percentage to target award 0.00%x_ShareBasedCompensationArrangementByShareBasedPaymentAwardTargetAward
/ us-gaap_AwardTypeAxis
= x_TotalStockholdersReturnTSRPerformanceBasedRestrictedStockMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
 
Total Shareholder Return (TSR) Performance Awards | Maximum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Vesting of performance awards as percentage to target award 200.00%x_ShareBasedCompensationArrangementByShareBasedPaymentAwardTargetAward
/ us-gaap_AwardTypeAxis
= x_TotalStockholdersReturnTSRPerformanceBasedRestrictedStockMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
 
Return On Capital Employed (ROCE) Performance Awards    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Share-based compensation plans, award vesting period 3 years  
Performance Period Weighting Year 1 20.00%x_PerformancePeriodWeightingYearOne
/ us-gaap_AwardTypeAxis
= x_ReturnOnCapitalEmployedROCEPerformanceBasedRestrictedStockMember
 
Performance Period Weighting Year 2 30.00%x_PerformancePeriodWeightingYearTwo
/ us-gaap_AwardTypeAxis
= x_ReturnOnCapitalEmployedROCEPerformanceBasedRestrictedStockMember
 
Performance Period Weighting Year 3 50.00%x_PerformancePeriodWeightingYearThree
/ us-gaap_AwardTypeAxis
= x_ReturnOnCapitalEmployedROCEPerformanceBasedRestrictedStockMember
 
Shares - Other than Stock Options 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= x_ReturnOnCapitalEmployedROCEPerformanceBasedRestrictedStockMember
259,280us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= x_ReturnOnCapitalEmployedROCEPerformanceBasedRestrictedStockMember
Return On Capital Employed (ROCE) Performance Awards | Threshold    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Vesting of performance awards as percentage to target award 50.00%x_ShareBasedCompensationArrangementByShareBasedPaymentAwardTargetAward
/ us-gaap_AwardTypeAxis
= x_ReturnOnCapitalEmployedROCEPerformanceBasedRestrictedStockMember
/ us-gaap_RangeAxis
= x_ThresholdMember
 
Return On Capital Employed (ROCE) Performance Awards | Target    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Vesting of performance awards as percentage to target award 100.00%x_ShareBasedCompensationArrangementByShareBasedPaymentAwardTargetAward
/ us-gaap_AwardTypeAxis
= x_ReturnOnCapitalEmployedROCEPerformanceBasedRestrictedStockMember
/ us-gaap_RangeAxis
= x_TargetMember
 
Return On Capital Employed (ROCE) Performance Awards | Minimum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Vesting of performance awards as percentage to target award 0.00%x_ShareBasedCompensationArrangementByShareBasedPaymentAwardTargetAward
/ us-gaap_AwardTypeAxis
= x_ReturnOnCapitalEmployedROCEPerformanceBasedRestrictedStockMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
 
Return On Capital Employed (ROCE) Performance Awards | Maximum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Vesting of performance awards as percentage to target award 200.00%x_ShareBasedCompensationArrangementByShareBasedPaymentAwardTargetAward
/ us-gaap_AwardTypeAxis
= x_ReturnOnCapitalEmployedROCEPerformanceBasedRestrictedStockMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember