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Summary of Significant Accounting Policies Summary of Significant Accounting Policies (A/R) (Table)
 12 Months Ended
Dec. 31, 2019
Receivables [Abstract]  
Allowance for doubtful accounts
The activity in the allowance for doubtful accounts was as follows (in millions): 
 
December 31,
 
2019
 
2018
 
2017
Beginning balance
$
1.5

 
$
7.0

 
$
0.9

Provision
(0.5
)
 
1.2

 
6.1

Write-offs, net
(0.1
)
 
(6.7
)
 
—

Ending balance
$
0.9

 
$
1.5

 
$
7.0