Retirement Benefits - Narrative (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2012	Mar. 31, 2011
Net periodic pension cost (credit) [Line Items]
UMWA obligation increase due to "Cadillac" plan excise tax	$ 6.0	$ 0
Retirement Benefit Plan Remeasurements [Abstract]
Defined Benefit Plan, Estimated Future Employer Contributions in Current Fiscal Year	22.5
Newly issued shares of common stock for contribution	361,446
Common stock value per share for stock contribution	$ 24.90
Aggregate value of shares of common stock contribution	9.0
2010 Healthcare reform black lung obligation increase	$ 0	$ 0

The pretax cost (credit) of benefit changes attributable to plan participants' prior service resulting from a plan amendment or plan initiation that occurred during the period. The cost has not yet been recognized in net periodic benefit cost. A plan amendment includes provisions that grant increased (decreased) benefits based on service rendered in prior periods.

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+ Details

- Definition

Pretax change in the value of either the benefit obligation or the plan assets resulting from experience different from that assumed or from a change in an actuarial assumption, or the consequence of a decision to temporarily deviate from the substantive plan, that has not been recognized in net periodic benefit cost.

+ References

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