Retirement Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Retirement Plans
Defined Contribution Plan, Cost Recognized	$ 74.5	$ 98.8	$ 156.7
Profit sharing component	$ 58.3	$ 73.6	$ 138.7
Percentage of employer's profit sharing contribution	8.00%	8.00%	8.00%
Employer's contribution to profit sharing plans for eligible employees	$ 46.7	$ 58.9	$ 108.1