Summary of Significant Accounting Policies Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Impact on results of operations	$ 239.0	$ 266.8	$ 241.6	$ 452.5	$ 243.9	$ 234.3	$ 235.7	$ 420.1	$ 1,199.9	$ 1,134.0	$ 1,059.3
Accounting Standards Update 2018-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment from adoption of ASU 2018-02											0.6
Impact on results of operations											0.0
Impact on cash flows											$ 0.0