Equity

Preferred Stock

We have 8.0 million shares of Preferred Stock authorized, of which 1.75 million shares are authorized as Series A, 1.0 million shares are authorized as Series X junior participating and 5.25 million shares are undesignated. Shares may be issued without a vote or action of shareholders from time to time in classes or series with the designations, powers, preferences, and the relative, participating, optional or other special rights of the shares of each such class or series and any qualifications, limitations or restrictions thereon as set forth in the instruments governing such shares. Any such Preferred Stock may rank prior to common stock as to dividend rights, liquidation preference or both, and may have full or limited voting rights and may be convertible into shares of common stock. No shares of Preferred Stock were issued and outstanding during 2017, 2016 and 2015.

Common Stock

The following table describes the number of shares authorized, issued and outstanding of our common stock as of December 31, 2017 and 2016:

As of December 31, 2017

As of December 31, 2016

(In millions)

Authorized

Issued

Outstanding

Authorized

Issued

Outstanding

Common stock

1,000.0

235.3

211.5

1,000.0

238.5

215.9

Share Repurchases

In July 2016 our Board of Directors authorized a program to repurchase up to $5.0 billion of our common stock (2016 Share Repurchase Program). This authorization does not have an expiration date. All share repurchases under this authorization will be retired. Under this authorization, we repurchased and retired 3.7 million and 3.3 million shares of common stock during the years ended December 31, 2017 and 2016, respectively, at a cost of $1.0 billion for each year. As of December 31, 2017, approximately $3.0 billion remains available for share repurchases under this authorization.

In May 2015 our Board of Directors authorized a program to repurchase up to $5.0 billion of our common stock (2015 Share Repurchase Program). All shares repurchased under this authorization were retired. Our 2015 Share Repurchase Program was completed as of December 31, 2015. Under this authorization, we repurchased and retired approximately 16.8 million shares of common stock at a cost of $5.0 billion during the year ended December 31, 2015.

In February 2011 our Board of Directors authorized a program to repurchase up to 20.0 million shares of our common stock (2011 Share Repurchase Program). Shares repurchased under this authorization were principally used to offset common stock issuances under our share-based compensation programs. Our 2011 Share Repurchase Program was completed as of March 31, 2017. Under this authorization, we repurchased 1.2 million shares of common stock at a cost of $365.4 million during the year ended December 31, 2017. We did not repurchase any shares of common stock under this authorization during the years ended December 31, 2016 and 2015.