v3.19.3.a.u2
Schedule II: Valuation and Qualifying Accounts
 12 Months Ended
Dec. 31, 2019
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]  
Schedule II: Valuation and Qualifying Accounts
Schedule II: Valuation and Qualifying Accounts
The table below details the activity of the allowance for doubtful accounts and sales credits for the years ended December 31, 2017, 2018 and 2019 (in millions):
 
Balance at
Beginning of
Year
 
Additions
 
Usage
 
Balance at
End of Year
Year ended December 31, 2017
$
467

 
$
1,131

 
$
(924
)
 
$
674

Year ended December 31, 2018
$
674

 
$
1,115

 
$
(1,060
)
 
$
729

Year ended December 31, 2019
$
729

 
$
1,481

 
$
(1,457
)
 
$
753


Note:
Additions to the allowance for doubtful accounts are charged to expense. Additions to the allowance for sales credits are charged against revenues.