Operations and Summary of Significant Accounting Policies (Recent Accounting Pronouncements) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect to stockholders' equity	$ (4,656.8)	$ (3,882.6)	$ (3,443.8)	$ (3,018.0)
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect to stockholders' equity		5.5
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect to stockholders' equity	$ (6,360.0)	(5,654.6)	$ (5,182.2)	$ (4,759.1)
Retained Earnings | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect to stockholders' equity		$ 5.5