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Retirement Benefits - Narrative (Details) (USD $)
In Millions, unless otherwise specified
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3 Months Ended |
12 Months Ended |
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Mar. 31, 2015
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Mar. 31, 2014
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Dec. 31, 2014
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| Amounts in AOCI to be recognized in retirement cost in next fiscal year [Abstract] |
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|
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| Benefit plan experience gains (losses) |
$ 14.2 |
$ 10.5 |
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| Other Benefit Plans [Abstract] |
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| Cash contributions |
|
|
87.2 |
| US Plans [Member] |
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|
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| Other Benefit Plans [Abstract] |
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|
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| Net periodic pension cost (credit) |
3.1 |
3.2 |
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| Non-US Plans [Member] |
|
|
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| Other Benefit Plans [Abstract] |
|
|
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| Net periodic pension cost (credit) |
7.3 |
6.9 |
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| UMWA Plans Postretirement Medical [Member] |
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|
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| Other Benefit Plans [Abstract] |
|
|
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| Net periodic pension cost (credit) |
2.4 |
1.8 |
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| Pension plan [Member] |
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|
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| Other Benefit Plans [Abstract] |
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|
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| Net periodic pension cost (credit) |
10.4 |
10.1 |
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| Retirement benefits other than pension [Member] |
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|
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| Other Benefit Plans [Abstract] |
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|
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| Net periodic pension cost (credit) |
4.3 |
3.0 |
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| Primary U.S. retirement plan [Member] |
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|
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| Retirement Benefit Plan Remeasurements [Abstract] |
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| Defined Benefit Plan, Estimated Future Employer Contributions in Current Fiscal Year |
$ 0 |
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