Employee Benefit Plans and Postretirement Benefits: Components of Pension Expense and Postretirement Expense (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefits earned during the year	$ 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 expense (income)	(1.8)	(0.3)
Postretirement Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Interest cost on benefit obligation	0.3	0.4
Amortization of net actuarial loss	0.2	0
Amortization of prior service credit	(1.3)	(1.7)
Plan curtailments	0	(9.5)
Net periodic benefit expense (income)	$ (0.8)	$ (10.8)