Equity (Tables)

12 Months Ended

Dec. 31, 2018

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, 2018, 2017 and 2016:

	As of December 31, 2018			As of December 31, 2017			December 31, 2016
(In millions)	Authorized	Issued	Outstanding	Authorized	Issued	Outstanding	Authorized	Issued	Outstanding
Common stock	1,000.0	221.0	197.2	1,000.0	235.3	211.5	1,000.0	238.5	215.9