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Schedule II - Valuation and Qualifying Accounts
 12 Months Ended
Dec. 31, 2011
Valuation and Qualifying Accounts [Abstract]  
SCHEDULE II VALUATION AND QUALIFYING ACCOUNTS
SCHEDULE II
VALUATION AND QUALIFYING ACCOUNTS

Allowance for Doubtful Accounts
 
Balance at Beginning of the Period
 
Expense
 
Deferral
 
Net Write-offs
 
Balance at End of the Period
 
 
(Millions of Dollars)
December 31, 2011
 
$
58.1

 
$
85.8

 
$
(35.9
)
 
$
(46.3
)
 
$
61.7

December 31, 2010
 
$
57.9

 
$
86.2

 
$
(32.5
)
 
$
(53.5
)
 
$
58.1

December 31, 2009
 
$
48.8

 
$
54.6

 
$
12.9

 
$
(58.4
)
 
$
57.9