Quarterly report pursuant to Section 13 or 15(d)

Shareholders' Equity (Schedule Of Stockholders' Equity) (Detail)

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Shareholders' Equity (Schedule Of Stockholders' Equity) (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Jun. 30, 2012
Jun. 30, 2011
Balance     $ 7,039.7 $ 3,838.7
Net income 274.3 427.4 665.7 850.8
Other comprehensive income (17.5) 26.4 5.7 51.0
Total comprehensive income     671.4 901.8
Equity offering       853.7
Purchase of additional noncontrolling interest       0.3
Stock and other incentive plans     2.3 3.1
Common stock dividends     (128.8) (38.0)
Purchase of subsidiary shares from noncontrolling interest       4.5
Undistributed gains to noncontrolling interest     8.6 9.6
Capital contribution by noncontrolling interest to subsidiary     22.3 0.2
Acquisition of controlling interest     (8.0) 947.6
Balance 7,607.5 6,521.5 7,607.5 6,521.5
Cliffs Shareholders' Equity [Member]
       
Balance     5,785.0 3,845.9
Net income     633.8 832.5
Other comprehensive income     2.7 50.1
Total comprehensive income     636.5 882.6
Equity offering       853.7
Purchase of additional noncontrolling interest       0.3
Stock and other incentive plans     2.3 3.1
Common stock dividends     (128.8) (38.0)
Balance 6,295.0 5,547.6 6,295.0 5,547.6
Non-controlling Interest [Member]
       
Balance     1,254.7 (7.2)
Net income     31.9 18.3
Other comprehensive income     3.0 0.9
Total comprehensive income     34.9 19.2
Purchase of subsidiary shares from noncontrolling interest       4.5
Undistributed gains to noncontrolling interest     8.6 9.6
Capital contribution by noncontrolling interest to subsidiary     22.3 0.2
Acquisition of controlling interest     (8.0) 947.6
Balance $ 1,312.5 $ 973.9 $ 1,312.5 $ 973.9
Bloom Lake [Member]
       
Percentage Of Ownership Interests 75.00% 75.00% 75.00% 75.00%
Tilden [Member]
       
Percentage Of Ownership Interests 85.00% 85.00% 85.00% 85.00%
Empire [Member]
       
Percentage Of Ownership Interests 79.00% 79.00% 79.00% 79.00%