Equity (Tables)

12 Months Ended

Dec. 31, 2017

Equity [Abstract]

Summary of 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