Employee Benefits (Tables)

9 Months Ended

Sep. 30, 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						9 Months Ended						12 Months Ended
	September 30,						September 30,						September 30,
	2015			2014			2015			2014			2015			2014
	(in millions)
Service cost	$	3.7		$	2.9		$	10.5		$	8.9		$	13.4		$	12.4
Interest cost	8.3			8.3			24.5			25.0			32.9			32.6
Expected return on plan assets	(12.3		)	(11.4		)	(35.6		)	(32.7		)	(46.5		)	(42.2		)
Prior service cost	0.1			0.1			0.1			0.4			0.3			0.7
Recognized net actuarial loss	6.3			3.7			17.7			11.6			21.5			18.8
Net pension cost	$	6.1		$	3.6		$	17.2		$	13.2		$	21.6		$	22.3

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

	3 Months Ended						9 Months Ended						12 Months Ended
	September 30,						September 30,						September 30,
	2015			2014			2015			2014			2015			2014
	(in millions)
Service cost	$	0.1		$	0.2		$	0.4		$	0.5		$	0.5		$	0.6
Interest cost	0.8			0.9			2.6			2.9			3.5			3.8
Expected return on plan assets	(0.7		)	(0.8		)	(2.3		)	(2.3		)	(3.0		)	(3.0		)
Recognized net actuarial loss (gain)	0.3			(0.1		)	0.9			0.5			1.1			1.3
Accretion of regulatory liability	0.3			0.2			0.7			0.6			0.9			0.6
Net postretirement benefit cost	$	0.8		$	0.4		$	2.3		$	2.2		$	3.0		$	3.3