Note 10. Employee Retirement Plans Amounts Recognized in OCI (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Gain (Loss), before Tax	$ 173.5
Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, Prior Service Cost (Credit), before Tax	1.5
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	2,378.9	$ 2,562.0	$ 4,858.0	$ 4,311.1
Defined Benefit Plan, Expected Amortization of Gain (Loss), Next Fiscal Year	6.0
Defined Benefit Plan, Expected Amortization in Next Fiscal Year, Net of Tax	4.6
Defined Benefit Plan, Expected Amortization of Prior Service Cost (Credit), Next Fiscal Year	1.2
Defined Benefit Plan, Expected Amortization of Prior Service Cost (Credit), Next Fiscal Year, Net of Tax	0.9
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, before Tax	(37.7)	(12.5)	5.2
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax	4.6	4.8	4.9
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), before Tax	(1.5)	0.0	0.0
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, before Tax	(34.6)	(7.7)	10.1
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax, Attributable to Parent	(7.9)	(1.8)	3.1
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	(26.7)	$ (5.9)	$ 7.0
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] | Terminal Funding Annuity [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Gain (Loss), before Tax	(170.1)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(131.2)
Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ (133.9)