Income Taxes (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Contingency [Line Items]
Investment tax credit effect on taxes		$ 100.0
Excess tax benefits, reduction in tax provision		11.6
Reduction in valuation allowance	$ 0.0	(17.2)	$ (4.6)
Federal and state benefits, reduction in tax provision		8.2
Income taxes paid, net of refunds received	$ 300.0	$ 124.0	$ 31.0
Bonus depreciation percentage on qualified assets	10000.00%	10000.00%	10000.00%
Net operating loss carryforwards	$ 87.0
Gross reduction in unrecognized tax benefits			$ 5.1
Unrecognized tax benefits if recognized that would impact effective tax rate	93.6	$ 93.3	93.0
Interest on income taxes accrued	0.8	0.8	4.0
Accrued liability for penalties	0.3	0.3	0.3
Accrued liability for interest related to uncertain tax positions and penalties	13.7	12.6	11.6
Equity Method Investment, Nonconsolidated Investee or Group of Investees
Income Tax Contingency [Line Items]
Tax credit related to investment	126.0
Accounting Standards Update 2016-02
Income Tax Contingency [Line Items]
Increase (decrease) in income tax provision			12.3
Various Tax Credits, Resolution of Tax Matters, and Change in Tax Rates
Income Tax Contingency [Line Items]
Increase (decrease) in income tax provision			13.0
Investment Tax Credit Carryforward
Income Tax Contingency [Line Items]
Increase (decrease) in income tax provision	126.0	$ 100.0	$ 84.0
State and Local Jurisdiction | SEC Schedule, 12-09, Valuation Allowance, Operating Loss Carryforward
Income Tax Contingency [Line Items]
Net operating loss carryforwards	$ 43.0