Accumulated Other Comprehensive Income: Accumulated Other Comprehensive (Loss) Income (Reclassifications) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other (income) expense, net	$ 1.7	$ (9.2)	$ 7.4	$ (10.2)
Income tax (expense) benefit	8.5	(54.2)	16.3	(323.0)
Net loss	(162.4)	(544.1)	(264.0)	(2,854.4)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net loss	(2.7)	(2.5)	(5.4)	(3.7)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Amortization of net unrealized gains on de-designated interest rate swaps
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Loss before income taxes	(3.3)	(3.0)	(6.6)	(4.2)
Income tax (expense) benefit	0.8	0.8	1.7	1.1
Net loss	(2.5)	(2.2)	(4.9)	(3.1)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Amortization of net actuarial loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other (income) expense, net	0.1	0.0	0.1	0.0
Reclassification out of Accumulated Other Comprehensive Income [Member] | Amortization of prior service credits
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other (income) expense, net	(0.3)	(0.3)	(0.6)	(0.7)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Pension and postretirement plans:
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Loss before income taxes	(0.2)	(0.3)	(0.5)	(0.7)
Income tax (expense) benefit	0.0	0.0	0.0	0.1
Net loss	(0.2)	(0.3)	(0.5)	(0.6)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Interest rate swaps | Amortization of net unrealized gains on de-designated interest rate swaps
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest (income) expense	$ (3.3)	$ (3.0)	$ (6.6)	$ (4.2)