Note 10. Employee Retirement Plans Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Defined Benefit Plan, Plan Assets, Amount	$ 548.5	$ 478.7	$ 488.0
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	100.00%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	100.00%
Cash and Cash Equivalents [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Defined Benefit Plan, Plan Assets, Amount	$ 13.5	$ 14.0
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	0.00%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	3.00%
Liability Hedging Portfolio [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	100.00%	90.00%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	92.00%
Growth Portfolio [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	0.00%	10.00%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	5.00%
US Treasury and Government [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Defined Benefit Plan, Plan Assets, Amount	$ 121.7	$ 77.1
Fixed Income Funds [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Defined Benefit Plan, Plan Assets, Amount	370.5	309.1
Asset-backed Securities [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Defined Benefit Plan, Plan Assets, Amount	2.2
Collateralized Mortgage Backed Securities [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Defined Benefit Plan, Plan Assets, Amount	4.1	2.1
Equity Funds [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Defined Benefit Plan, Plan Assets, Amount	29.1	69.7
Fixed Income Investments [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Defined Benefit Plan, Plan Assets, Amount	7.4	6.7
Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Defined Benefit Plan, Plan Assets, Amount	13.5	14.0
Fair Value, Inputs, Level 1 [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Defined Benefit Plan, Plan Assets, Amount	13.5	14.0
Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Defined Benefit Plan, Plan Assets, Amount	527.6	458.0
Fair Value, Inputs, Level 2 [Member] | US Treasury and Government [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Defined Benefit Plan, Plan Assets, Amount	121.7	77.1
Fair Value, Inputs, Level 2 [Member] | Fixed Income Funds [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Defined Benefit Plan, Plan Assets, Amount	370.5	309.1
Fair Value, Inputs, Level 2 [Member] | Asset-backed Securities [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Defined Benefit Plan, Plan Assets, Amount	2.2
Fair Value, Inputs, Level 2 [Member] | Collateralized Mortgage Backed Securities [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Defined Benefit Plan, Plan Assets, Amount	4.1	2.1
Fair Value, Inputs, Level 2 [Member] | Equity Funds [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Defined Benefit Plan, Plan Assets, Amount	29.1	69.7
Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Defined Benefit Plan, Plan Assets, Amount	7.4	6.7
Fair Value, Inputs, Level 3 [Member] | Fixed Income Investments [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Defined Benefit Plan, Plan Assets, Amount	$ 7.4	$ 6.7