Benefits (Tables)

6 Months Ended

Jun. 30, 2015

Benefits (Tables) [Abstract]

Components of net periodic pension and OPEB costs

	Pension Costs
	Three Months Ended June 30						Six Months Ended June 30
Benefit Plan Cost Components	2015			2014			2015			2014
	(Millions of Dollars)
Net Periodic Benefit Cost
Service cost	$	3.9		$	2.3		$	7.8		$	5.0
Interest cost	15.1			17.0			30.3			34.1
Expected return on plan assets	(25.6		)	(24.6		)	(51.4		)	(49.3		)
Amortization of:
Prior service cost	0.5			0.5			1.0			1.0
Actuarial loss	11.4			9.3			23.0			18.4
Net Periodic Benefit Cost	$	5.3		$	4.5		$	10.7		$	9.2

	OPEB Costs
	Three Months Ended June 30						Six Months Ended June 30
Benefit Plan Cost Components	2015			2014			2015			2014
	(Millions of Dollars)
Net Periodic Benefit Cost
Service cost	$	2.1		$	2.1		$	4.7		$	4.3
Interest cost	3.9			4.4			8.1			8.9
Expected return on plan assets	(5.9		)	(6.0		)	(11.8		)	(11.9		)
Amortization of:
Transition obligation	—			—			—			—
Prior service (credit)	(0.3		)	(0.4		)	(0.6		)	(0.9		)
Actuarial loss	0.5			0.4			1.0			0.6
Net Periodic Benefit Cost	$	0.3		$	0.5		$	1.4		$	1.0