Basis of Presentation - Changes to Quarterly Results: Balance Sheet (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020		Mar. 31, 2020	[2]	Jan. 01, 2020	Dec. 31, 2019	[2]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Total Assets as of December 31, 2020	$ 9,924.9	$ 9,220.3	[1]
Total Liabilities as of December 31, 2020	6,246.7	5,636.4	[1]
Total Equity as of December 31, 2020	$ 3,678.2	3,583.9	[1]	$ 1,595.4		$ 1,577.3	$ 1,577.3
As Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Total Assets as of December 31, 2020		9,219.4
Total Liabilities as of December 31, 2020		5,641.7
Total Equity as of December 31, 2020		3,577.7				1,577.7
Increase (Decrease)
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Total Assets as of December 31, 2020		0.9
Total Liabilities as of December 31, 2020		(5.3)
Total Equity as of December 31, 2020		$ 6.2				$ (0.4)

[1] See discussion in Note 1 - Basis of Presentation for further detail regarding the elimination of the International lag reporting.

[2] See discussion in Note 1 - Basis of Presentation for further detail regarding the elimination of the International lag reporting.