We compute basic earnings per share, or Basic EPS, by dividing net income (loss) by the weighted average number of common shares outstanding during the period. We compute the weighted average number of common shares outstanding during the reporting period using the total of common stock and Class B common stock outstanding as of the last day of the previous year end reporting period plus the weighted average of any additional shares issued and outstanding less the weighted average of any common shares repurchased during the reporting period.

Diluted earnings per share, or Diluted EPS, includes the potential dilution of common equivalent shares outstanding that could occur from stock-based awards and other stock-based commitments using the treasury stock

method. We compute Diluted EPS by dividing net income (loss) by the sum of the weighted average number of common and common equivalent shares outstanding during the period. We computed the weighted average number of common and common equivalent shares outstanding during the period using the sum of (i) the number of shares of common stock and Class B common stock used in the Basic EPS calculation as indicated above, and (ii) if dilutive, the incremental weighted average common stock that we would issue upon the assumed exercise of outstanding common equivalent shares, primarily related to stock options and the vesting of restricted stock units using the treasury stock method, and (iii) if dilutive, performance-based and market-based awards based on the number of shares that would be issuable as of the end of the reporting period assuming the end of the reporting period was also the end of the contingency period.

Under the treasury stock method, the assumed proceeds calculation includes the actual proceeds to be received from the employee upon exercise of outstanding equity awards and the average unrecognized compensation cost during the period. The treasury stock method assumes that a company uses the proceeds from the exercise of an equity award to repurchase common stock at the average market price for the reporting period.

In periods of a net loss, common equivalent shares are excluded from the calculation of Diluted EPS as their inclusion would have an antidilutive effect. Accordingly, for periods in which we report a net loss, such as for the year ended December 31, 2020, Diluted EPS is the same as Basic EPS, since dilutive common equivalent shares are not assumed to have been issued if their effect is anti-dilutive.

Below is a reconciliation of the weighted average number of shares of common stock outstanding in calculating Diluted EPS (shares in thousands and dollars in millions, except per share amounts) for the periods presented:

	Year ended December 31,
	2020			2019		2018
Numerator:
Net income (loss)	$	(289	)	$	126	$	113
Denominator:
Weighted average shares used to compute Basic EPS		134,858			138,975		138,116
Weighted average effect of dilutive securities:
Stock options		—			155		351
RSUs/MSUs		—			1,528		1,908
Weighted average shares used to compute Diluted EPS		134,858			140,658		140,375
Basic EPS	$	(2.14	)	$	0.91	$	0.82
Diluted EPS	$	(2.14	)	$	0.89	$	0.81

Potential common shares, consisting of outstanding stock options, RSUs, and MSUs, totaling approximately 13.7 million, 6.7 million, and 6.2 million, for the years ended December 31, 2020, 2019 and 2018, respectively, have been excluded from the calculations of Diluted EPS because their effect would have been antidilutive. In addition, potential common shares of certain performance-based awards of approximately 0.2 million, 0.7 million, and 0.5 million, for the years ended December 31, 2020, 2019 and 2018, respectively, for which all targets required to trigger vesting had not been achieved, were excluded from the calculation of weighted average shares used to compute Diluted EPS for those reporting periods.

The earnings per share amounts are the same for common stock and Class B common stock because the holders of each class are legally entitled to equal per share distributions whether through dividends or in liquidation. In addition, our non-vested RSUs and MSUs are entitled to dividend equivalents, which will be payable to the holder subject to, and only upon vesting of, the underlying awards and are therefore forfeitable. Given such dividend equivalents are forfeitable, we do not consider them to be participating securities and, consequently, they are not subject to the two‑class method of determining earnings per share.