Pension and Other Postretirement Benefits (Tables)

9 Months Ended

Sep. 30, 2017

Compensation and Retirement Disclosure [Abstract]

Net periodic pension and OPEB cost

Pension and Other Postretirement Benefits("OPEB")

	For the Three Months Ended
	September 30, 2017								September 30, 2016
	Pension			OPEB		Consolidated			Pension			OPEB		Consolidated
	(In millions)
Net periodic pension and OPEB cost (benefit):
Service cost	$	1.9		$	2.6	$	4.5		$	1.9		$	0.4	$	2.3
Interest cost	51.8			7.7		59.5			31.0			1.5		32.5
Expected return on plan assets	(68.2		)	0.1		(68.1		)	(38.0		)	—		(38.0		)
Amortization of prior service cost (benefit)	0.2			—		0.2			0.2			0.1		0.3
Amortization of net actuarial loss (gain)	8.1			—		8.1			7.4			—		7.4
Less: expected participant contributions	(0.2		)	—		(0.2		)	(0.1		)	—		(0.1		)
Net periodic pension and OPEB cost (benefit)	$	(6.4	)	$	10.4	$	4.0		$	2.4		$	2.0	$	4.4

	For the Nine Months Ended
	September 30, 2017									September 30, 2016
	Pension			OPEB			Consolidated			Pension			OPEB		Consolidated
	(In millions)
Net periodic pension and OPEB cost (benefit):
Service cost	$	5.6		$	8.0		$	13.6		$	5.7		$	1.6	$	7.3
Interest cost	154.1			22.9			177.0			95.5			4.4		99.9
Expected return on plan assets	(201.1		)	0.2			(200.9		)	(118.0		)	—		(118.0		)
Amortization of prior service cost (benefit)	0.5			—			0.5			0.6			—		0.6
Amortization of net actuarial loss (gain)	20.9			—			20.9			23.0			—		23.0
Curtailment loss (gain)	—			(2.9		)	(2.9		)	—			—		—
Less: expected participant contributions	(0.5		)	—			(0.5		)	(0.4		)	—		(0.4		)
Net periodic pension and OPEB cost (benefit)	$	(20.5	)	$	28.2		$	7.7		$	6.4		$	6.0	$	12.4