Net Income Per Share

The components of basic and diluted net income per share attributable to common stockholders are as follows:



	Three Months Ended March 31,
	2019			2018
	(in millions)
Net income attributable to common stockholders	$	350		$	178
Participating share-based earnings	(2		)	(1		)
Basic and diluted net income attributable to common stockholders	$	348		$	177

Basic weighted average shares outstanding is reconciled to diluted weighted average shares outstanding as follows:



	Three Months Ended March 31,
	2019	2018
	(in millions)
Basic weighted average shares outstanding	169	170
Dilution attributable to stock-based compensation awards	—	1
Diluted weighted average shares outstanding	169	171

Stock repurchase program. In December 2018, the Company's board of directors authorized a $2 billion common stock repurchase program. Under this stock repurchase program, the Company may repurchase shares at management's discretion in accordance with applicable securities laws. In addition, the Company may repurchase shares pursuant to a trading plan meeting the requirements of Rule 10b5-1 under the Securities Act of 1934, which would permit the Company to repurchase shares at times that may otherwise be prohibited under the Company's insider trading policy. The stock repurchase program has no time limit, may be modified, suspended or terminated at any time by the board of directors and replaced and terminated the Company's prior $100 million common stock repurchase program announced in February 2018.

During the three months ended March 31, 2019 and 2018, the Company repurchased $200 million and $17 million, respectively, of common stock under these repurchase programs. As of March 31, 2019, $1.7 billion remains available for use to repurchase shares under the Company's common stock repurchase program.