Note 10. Employee Retirement Plans Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Defined Benefit Plan, Plan Assets, Amount	$ 23.6	$ 548.5	$ 478.7
Cash and Cash Equivalents [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	100.00%
Defined Benefit Plan, Plan Assets, Amount		$ 13.5
Liability Hedging Portfolio [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		100.00%
US Treasury and Government [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Defined Benefit Plan, Plan Assets, Amount		$ 121.7
Fixed Income Funds [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Defined Benefit Plan, Plan Assets, Amount		370.5
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
Equity Funds [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Defined Benefit Plan, Plan Assets, Amount		29.1
Fixed Income Investments [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Defined Benefit Plan, Plan Assets, Amount		7.4
Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Defined Benefit Plan, Plan Assets, Amount		13.5
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	$ 23.6	13.5
Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Defined Benefit Plan, Plan Assets, Amount		527.6
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
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
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
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
Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Defined Benefit Plan, Plan Assets, Amount		7.4
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