EMPLOYEE BENEFIT PLANS - AMOUNTS RECOGNIZED IN CONSOLIDATED BALANCE SHEETS (DETAILS) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Pension and Other Postretirement Defined Benefit Plans, Liabilities [Abstract]
Accrued benefit liability-long term	$ 463.4	$ 367.1
Qualified Defined Benefit [Member]
Pension and Other Postretirement Defined Benefit Plans, Liabilities [Abstract]
Accrued benefit liability-current	0	0
Accrued benefit liability-long term	306.3	200.3
Total liability recognized	306.3	200.3
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Abstract]
Prior service cost (credit)	(15.7)	(16.7)
Net loss	613.2	417.0
Amount recognized in AOCI (pretax)	597.5	400.3
Nonqualified Defined Benefit [Member]
Pension and Other Postretirement Defined Benefit Plans, Liabilities [Abstract]
Accrued benefit liability-current	2.2	2.3
Accrued benefit liability-long term	40.6	38.8
Total liability recognized	42.8	41.1
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Abstract]
Prior service cost (credit)	0	0.1
Net loss	11.5	8.7
Amount recognized in AOCI (pretax)	11.5	8.8
Postretirement Medical Benefits [Member]
Pension and Other Postretirement Defined Benefit Plans, Liabilities [Abstract]
Accrued benefit liability-current	4.1	4.9
Accrued benefit liability-long term	116.1	127.6
Total liability recognized	120.2	132.5
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Abstract]
Prior service cost (credit)	2.2	2.5
Net loss	(3.8)	20.3
Amount recognized in AOCI (pretax)	$ (1.6)	$ 22.8