ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Tables)

12 Months Ended

Dec. 31, 2017

ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS).

Schedule of changes in accumulated other comprehensive income (loss) by component, net of tax

					Non-				Accumulated
			Post-		Qualified				Other
	Pension		Retirement		Pension				Comprehensive
(In millions)	Benefits		Benefits		Benefits		Other		Income (Loss)
Balance at December 31, 2015	$	(41.7)	$	(4.7)	$	(0.2)	$	(0.3)	$	(46.9)
Net gain (loss) in prior service costs		—		24.1		(0.1)		0.1		24.1
Amortization of prior service cost		(1.4)		(0.9)		(0.1)		0.2		(2.2)
Amortization of net loss (gain)		1.7		(0.4)		—		(0.1)		1.2
Other adjustments		—		—		—		0.2		0.2
Balance at December 31, 2016		(41.4)		18.1		(0.4)		0.1		(23.6)
Net gain in prior service costs		—		0.7		—		0.1		0.8
Amortization of prior service cost		(1.4)		(2.5)		(0.1)		—		(4.0)
Amortization of net loss (gain)		2.2		(0.7)		0.2		—		1.7
Other adjustments		—		—		—		0.2		0.2
Balance at December 31, 2017	$	(40.6)	$	15.6	$	(0.3)	$	0.4	$	(24.9)