Pension and Other Postretirement Benefits (Tables)

6 Months Ended

Jun. 30, 2017

Compensation and Retirement Disclosure [Abstract]

Net periodic pension and OPEB cost

Pension and Other Postretirement Benefits("OPEB")

	For the Three Months Ended
	June 30, 2017								June 30, 2016
	Pension			OPEB		Consolidated			Pension			OPEB			Consolidated
	(In millions)
Net periodic pension and OPEB cost (benefit):
Service cost	$	1.9		$	2.8	$	4.7		$	2.0		$	0.6		$	2.6
Interest cost	50.8			7.6		58.4			32.6			1.6			34.2
Expected return on plan assets	(66.8		)	—		(66.8		)	(40.5		)	—			(40.5		)
Amortization of prior service cost (benefit)	0.1			—		0.1			0.2			(0.1		)	0.1
Amortization of net actuarial loss (gain)	7.8			—		7.8			7.9			—			7.9
Less: expected participant contributions	(0.1		)	—		(0.1		)	(0.2		)	—			(0.2		)
Net periodic pension and OPEB cost (benefit)	$	(6.3	)	$	10.4	$	4.1		$	2.0		$	2.1		$	4.1

	For the Six Months Ended
	June 30, 2017									June 30, 2016
	Pension			OPEB			Consolidated			Pension			OPEB			Consolidated
	(In millions)
Net periodic pension and OPEB cost (benefit):
Service cost	$	3.7		$	5.4		$	9.1		$	3.8		$	1.2		$	5.0
Interest cost	102.3			15.2			117.5			64.5			2.9			67.4
Expected return on plan assets	(132.9		)	0.1			(132.8		)	(80.0		)	—			(80.0		)
Amortization of prior service cost (benefit)	0.3			—			0.3			0.4			(0.1		)	0.3
Amortization of net actuarial loss (gain)	12.8			—			12.8			15.6			—			15.6
Curtailment (gain)	—			(2.9		)	(2.9		)	—			—			—
Less: expected participant contributions	(0.3		)	—			(0.3		)	(0.3		)	—			(0.3		)
Net periodic pension and OPEB cost (benefit)	$	(14.1	)	$	17.8		$	3.7		$	4.0		$	4.0		$	8.0