Employee Benefits (Tables)

3 Months Ended

Mar. 31, 2015

Compensation and Retirement Disclosure [Abstract]

Schedule of Defined Benefit Plans Disclosures

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,
	2015			2014			2015			2014
	(in millions)
Service cost	$	3.4		$	3.0		$	12.2		$	13.4
Interest cost	8.1			8.4			33.1			31.2
Expected return on plan assets	(11.6		)	(10.6		)	(44.6		)	(39.2		)
Prior service cost	—			0.1			0.5			0.9
Recognized net actuarial loss	5.7			3.9			17.2			26.0
Net pension cost	$	5.6		$	4.8		$	18.4		$	32.3

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

	3 Months Ended						12 Months Ended
	March 31,						March 31,
	2015			2014			2015			2014
	(in millions)
Service cost	$	0.2		$	0.2		$	0.6		$	0.7
Interest cost	0.9			1.0			3.7			3.7
Expected return on plan assets	(0.8		)	(0.8		)	(3.0		)	(2.7		)
Recognized net actuarial loss (gain)	0.3			0.3			0.7			2.6
Accretion of regulatory liability	0.2			0.2			0.8			0.5
Net postretirement benefit cost	$	0.8		$	0.9		$	2.8		$	4.8