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Stock Purchase Plan (Details)
$ in Millions
 12 Months Ended
Dec. 31, 2019
USD ($)
employee
shares
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Share-based Payment Arrangement [Abstract]      
Number of employees contributing to company's ESOP | employee 41,946    
Participants percentage contribution on a pretax basis only of their annual compensation (up to the lesser of) 20.00%    
Percentage of matching contribution to ESOP Plan by employer 100.00%    
Percentage of eligible contribution plan up to which employer contributes (up to) 6.00%    
Company contributions to ESOP on behalf of participating employees representing amounts authorized by employees to be withheld from their earnings on pre-tax basis $ 180.5 $ 170.3 $ 138.7
Company's matching contributions to the ESOP $ 111.9 $ 104.7 $ 90.7
Employee stock ownership plan common stock shares held in ESOP (in shares) | shares 8,433,722    
Percentage of total voting shares outstanding held by the ESOP 9.20%