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Pension and Other Postretirement Benefits - Additional Information (Detail) (USD $) In Millions, unless otherwise specified | 0 Months Ended | 3 Months Ended | 6 Months Ended | 9 Months Ended |  |  |  | 3 Months Ended | 9 Months Ended |  |  | 3 Months Ended
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Dec. 31, 2015 Scenario, Forecast [Member] | Dec. 31, 2014 Scenario, Forecast [Member] | Jun. 06, 2014 United Steelworkers Labor Agreement [Member] | May 31, 2014 United Steelworkers Labor Agreement [Member] | Sep. 30, 2014 United Steelworkers Labor Agreement [Member] | Jun. 30, 2014 United Steelworkers Labor Agreement [Member] | Sep. 30, 2014 United Steelworkers Labor Agreement [Member] | Jun. 06, 2014 United Steelworkers Labor Agreement [Member] Employees Location | May 31, 2014 United Steelworkers Labor Agreement [Member] | Dec. 31, 2013 United Steelworkers Labor Agreement [Member] | Dec. 31, 2014 United Steelworkers Labor Agreement [Member] Scenario, Forecast [Member] | Sep. 30, 2014 Postretirement Benefit Plan [Member] | Sep. 30, 2014 Postretirement Benefit Plan [Member] | Aug. 31, 2014 Postretirement Benefit Plan [Member] | Dec. 31, 2013 Postretirement Benefit Plan [Member] | Dec. 31, 2014 Postretirement Benefit Plan [Member] Scenario, Forecast [Member]
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Term of labor agreement, in years |  |  | 5 years |  |  |  |  |  |  |  |  |  |  |  |  |
Number of employees covered by labor agreement |  |  |  |  |  |  |  | 6,100 |  |  |  |  |  |  |  |
Number of locations affected by labor agreement |  |  |  |  |  |  |  | 10 |  |  |  |  |  |  |  |
Labor agreement expired, date |  |  |  |  |  |  | May 15, 2014 |  |  |  |  |  |  |  |  |
Pretax costs related to preparation for and ratification of new agreement |  |  |  |  |  |  | $ 18 |  |  |  |  |  |  |  |  |
After-tax costs related to preparation for and ratification of new agreement |  |  |  |  |  |  | 12 |  |  |  |  |  |  |  |  |
Discount rate used to determine pension benefit obligation |  |  |  |  |  |  |  |  | 4.25% | 4.80% |  |  |  | 4.15% | 4.80% |
Increase in pension liability, plan amendment |  |  |  | 100 |  |  |  |  |  |  |  |  |  |  |  |
Accumulated (increase) decrease in net actuarial loss after-tax, plan amendment |  |  |  |  |  | (65) |  |  |  |  |  |  | 59 |  |  |
Annual decrease in net periodic benefit cost, plan amendment |  |  |  |  | 6 | 13 | 8 |  |  |  | 5 | 2 | 7 |  |  | 5
Pension contributions minimum required | 125 | 100 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Decrease in other post benefit liability |  |  |  |  |  |  |  |  |  |  |  |  | $ 90 |  |  |

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- Definition The after-tax amount of costs an entity incurs due to the preparation for and ratification of a new union labor agreement. This may include costs for the preparation of a potential strike, upfront, one-time signing bonuses or other similar benefits upon ratification of new agreement, charges related to actuarial changes in pension and other postretirement benefit plans due to the provisions of the new agreement, etc. + References No definition available. + Details
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- Definition The amount of costs an entity incurs due to the preparation for and ratification of a new union labor agreement. This may include costs for the preparation of a potential strike, upfront, one-time signing bonuses or other similar benefits upon ratification of new agreement, charges related to actuarial changes in pension and other postretirement benefit plans due to the provisions of the new agreement, etc. + References No definition available. + Details
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- Definition Defined Benefit Plan Minimum Required Funding Increase Decrease. + References No definition available. + Details
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- Definition Labor Agreement Expiration Date + References No definition available. + Details
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- Definition Number of employees covered by labor agreement + References No definition available. + Details
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- Definition Number of locations affected by labor agreement + References No definition available. + Details
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- Definition Term of labor agreement + References No definition available. + Details
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- Definition The interest rate used to adjust for the time value of money for the plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(1) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Details
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- Definition The increase (decrease) during the reporting period in the amount due to fund pension and non-pension benefits to employees, retired and disabled former employees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 + Details
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- Definition The increase (decrease) during the reporting period in the amount due to fund retirement benefits to employees, retired and disabled former employees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 + Details
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- Definition Amount after tax of cost (credit) of benefit changes attributable to plan participants' prior service resulting from a plan amendment or plan initiation that has not been recognized in net periodic benefit cost (credit). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e637-108580 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669646-108580 + Details
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- Definition Amount after tax of (increase) decrease in the value of the projected benefit obligation related to a change in an actuarial assumption and increase (decrease) in the value of the plan assets resulting from experience different from that assumed, that has not been recognized in net periodic benefit (cost) credit. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e637-108580 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669646-108580 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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