Goodwill and Other Intangible Assets: - Schedule of Finite-Lived Intangible Assets, Future Amortization (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization expense for intangible assets subject to amortization	$ 171.0	$ 225.8	$ 241.0
Finite-Lived Intangible Assets, Amortization Expense, Maturity Schedule [Abstract]
2019	133.5
2020	100.8
2021	71.0
2022	58.6
2023	53.5
Thereafter	624.7
Total	$ 1,042.1	$ 1,213.1