Employee Benefits (Tables)

6 Months Ended

Jun. 30, 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						6 Months Ended						12 Months Ended
	June 30,						June 30,						June 30,
	2016			2015			2016			2015			2016			2015
	(in millions)
Service cost	$	0.1		$	0.1		$	0.2		$	0.3		$	0.5		$	0.6
Interest cost	0.9			0.9			1.8			1.8			3.5			3.6
Expected return on plan assets	(0.7		)	(0.8		)	(1.4		)	(1.6		)	(3.0		)	(3.1		)
Recognized net actuarial loss	0.3			0.3			0.5			0.6			1.1			0.7
Accretion of regulatory liability	0.2			0.2			0.4			0.4			1.0			0.8
Net postretirement benefit cost	$	0.8		$	0.7		$	1.5		$	1.5		$	3.1		$	2.6

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

	3 Months Ended						6 Months Ended						12 Months Ended
	June 30,						June 30,						June 30,
	2016			2015			2016			2015			2016			2015
	(in millions)
Service cost	$	3.1		$	3.4		$	6.1		$	6.8		$	13.1		$	12.6
Interest cost	8.1			8.1			16.3			16.2			32.8			32.9
Expected return on plan assets	(12.1		)	(11.7		)	(24.3		)	(23.3		)	(48.7		)	(45.6		)
Prior service cost	—			—			—			—			0.1			0.3
Recognized net actuarial loss	3.7			5.7			7.5			11.4			18.0			18.9
Settlement costs	1.1			—			1.1			—			17.8			—
Net pension cost	$	3.9		$	5.5		$	6.7		$	11.1		$	33.1		$	19.1