High CV Thermal CO/Coal/Underground Mining [Member] High CV Thermal CO/Coal/Underground Mining High CV Thermal PA/Coal/Underground Mining [Member] High CV Thermal PA/Coal/Underground Mining Metallurgical WV/Coal/Underground Mining [Member] Metallurgical WV/Coal/Underground Mining U.S. Federal Government [Member] UNITED STATES Powder River Basin WY/Coal/Open Pit [Member] Powder River Basin WY/Coal/Open Pit Coal [Member] High CV Thermal [Member] Metallurgical [Member] Powder River Basin [Member] Other [Member] Corporate and Other [Member]