Employee Benefit Plans and Postretirement Benefits: (Tables)

3 Months Ended

Mar. 31, 2015

Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]

Pension And Other Postretirement Benefits, Net Periodic Benefit Costs, Disclosure

The components of pension benefit income (including provision for executive retirement agreements) were as follows for the three month periods ended March 31:

	Three Months Ended
(Millions)	2015			2014
Benefits earned during the period	$	2.4		$	2.2
Interest cost on benefit obligation	13.4			14.7
Expected return on plan assets	(17.6		)	(17.2		)
Net periodic benefit income	$	(1.8	)	$	(0.3	)

The components of postretirement benefits income were as follows for the three month periods ended March 31:

	Three Months Ended
(Millions)	2015			2014
Interest cost on benefit obligation	$	0.3		$	0.4
Amortization of net actuarial loss	0.2			—
Amortization of prior service credit	(1.3		)	(1.7		)
Plan curtailments	—			(9.5		)
Net periodic benefit income	$	(0.8	)	$	(10.8	)