PENSION AND OTHER POST-RETIREMENT BENEFIT PLANS - COMPONENTS OF NET PERIODIC BENEFIT COST (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension Benefits
Amounts recognized in net periodic benefit cost
Service cost	$ 28,300	$ 26,935	$ 31,339
Interest cost	44,179	48,886	43,962
Expected return on plan assets	(68,830)	(74,080)	(73,128)
Amortization of prior service (credit) cost	(1,178)	(667)	422
Amortization of net loss (gain)	30,510	23,360	40,397
Curtailment credit	(688)	0	(364)
Settlement loss	23,067	0	18
Total net periodic benefit cost	55,360	24,434	42,646
Change in plan assets and benefit obligations recognized in AOCI, pre-tax
Actuarial net (gain) loss	(21,554)	99,136	(230,605)
Prior service (credit) cost	1,748	833	(613)
Total recognized in other comprehensive (income) loss, pre-tax	(19,806)	99,969	(231,218)
Net amounts recognized in periodic benefit cost and AOCI	35,554	124,403	(188,572)
Other Benefits
Amounts recognized in net periodic benefit cost
Service cost	542	706	1,094
Interest cost	10,187	11,696	10,747
Expected return on plan assets	0	0	0
Amortization of prior service (credit) cost	611	616	618
Amortization of net loss (gain)	(57)	(141)	(73)
Curtailment credit	204	0	0
Settlement loss	0	0	0
Total net periodic benefit cost	11,487	12,877	12,386
Change in plan assets and benefit obligations recognized in AOCI, pre-tax
Actuarial net (gain) loss	(26,270)	36,021	(33,165)
Prior service (credit) cost	(834)	(629)	(632)
Total recognized in other comprehensive (income) loss, pre-tax	(27,104)	35,392	(33,797)
Net amounts recognized in periodic benefit cost and AOCI	$ (15,617)	$ 48,269	$ (21,411)