Benefits (Tables)

6 Months Ended

Jun. 30, 2011

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	2011			2010			2011			2010
	(Millions of Dollars)
Net Periodic Benefit Cost
Service cost	$	3.3		$	4.9		$	7.9		$	11.8
Interest cost	17.1			16.4			33.8			33.8
Expected return on plan assets	(20.4		)	(19.0		)	(41.1		)	(38.7		)
Amortization of:
Prior service cost	0.5			0.5			1.1			1.1
Actuarial loss	9.0			6.7			17.1			13.3
Net Periodic Benefit Cost	$	9.5		$	9.5		$	18.8		$	21.3

	OPEB Costs
	Three Months Ended June 30						Six Months Ended June 30
Benefit Plan Cost Components	2011			2010			2011			2010
	(Millions of Dollars)
Net Periodic Benefit Cost
Service cost	$	2.4		$	2.8		$	5.2		$	5.6
Interest cost	5.1			5.1			10.4			10.5
Expected return on plan assets	(4.1		)	(3.6		)	(8.4		)	(7.2		)
Amortization of:
Transition obligation	0.1			0.1			0.2			0.2
Prior service (credit)	(0.5		)	(2.9		)	(1.0		)	(5.9		)
Actuarial loss	1.5			2.7			3.0			5.4
Net Periodic Benefit Cost	$	4.5		$	4.2		$	9.4		$	8.6