Employee Benefits (Tables)

3 Months Ended

Mar. 31, 2016

Compensation and Retirement Disclosure [Abstract]

Schedule of Defined Benefit Plans Disclosures

Net periodic postretirement benefit cost components are listed in the table below:

	3 Months Ended						12 Months Ended
	March 31,						March 31,
	2016			2015			2016			2015
	(in millions)
Service cost	$	0.1		$	0.2		$	0.5		$	0.6
Interest cost	0.9			0.9			3.5			3.7
Expected return on plan assets	(0.7		)	(0.8		)	(3.1		)	(3.0		)
Recognized net actuarial loss	0.2			0.3			1.1			0.7
Accretion of regulatory liability	0.2			0.2			1.0			0.8
Net postretirement benefit cost	$	0.7		$	0.8		$	3.0		$	2.8

Components of the qualified and nonqualified net periodic pension cost are listed in the table below:

	3 Months Ended						12 Months Ended
	March 31,						March 31,
	2016			2015			2016			2015
	(in millions)
Service cost	$	3.0		$	3.4		$	13.4		$	12.2
Interest cost	8.2			8.1			32.8			33.1
Expected return on plan assets	(12.2		)	(11.6		)	(48.3		)	(44.6		)
Prior service cost	—			—			0.1			0.5
Recognized net actuarial loss	3.8			5.7			20.0			17.2
Pension settlement costs	—			—			16.7			—
Net pension cost	$	2.8		$	5.6		$	34.7		$	18.4