Employee Benefits (Tables)

6 Months Ended

Jun. 30, 2016

Compensation and Retirement Disclosure [Abstract]

Schedule of the components of net periodic benefit cost

The following tables show the components of net periodic pension and OPEB costs for our benefit plans. Our pension and OPEB costs for the three and six months ended June 30, 2016, include costs attributable to the Integrys pension and OPEB plans. The terms and conditions of the legacy company plans have not changed materially since the acquisition.

	Pension Costs
	Three Months Ended June 30						Six Months Ended June 30
(in millions)	2016			2015			2016			2015
Service cost	$	10.7		$	3.9		$	22.0		$	7.8
Interest cost	33.0			15.1			66.2			30.3
Expected return on plan assets	(49.0		)	(25.6		)	(98.0		)	(51.4		)
Loss on plan settlement	14.1			—			14.1			—
Amortization of prior service cost	0.8			0.5			1.7			1.0
Amortization of net actuarial loss	20.2			11.4			40.7			23.0
Net periodic benefit cost	$	29.8		$	5.3		$	46.7		$	10.7

	OPEB Costs
	Three Months Ended June 30						Six Months Ended June 30
(in millions)	2016			2015			2016			2015
Service cost	$	6.4		$	2.1		$	13.1		$	4.7
Interest cost	9.3			3.9			18.5			8.1
Expected return on plan assets	(13.3		)	(5.9		)	(26.4		)	(11.8		)
Amortization of prior service credit	(2.4		)	(0.3		)	(4.7		)	(0.6		)
Amortization of net actuarial loss	1.9			0.5			4.2			1.0
Net periodic benefit cost	$	1.9		$	0.3		$	4.7		$	1.4