Parent Only Statements - Balance Sheets - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]
Preferred stock, stated value (in dollars per share)	$ 0.20	$ 0.20
Preferred stock, shares authorized (in shares)	20,000,000	20,000,000
Common stock, par value (in dollars per share)	$ 0.20	$ 0.20
Common stock, shares authorized (in shares)	1,125,000,000	1,125,000,000
Common stock, shares issued (in shares)	443,500,000	436,600,000
Accumulated other comprehensive loss tax benefit	$ 1,696	$ (5,364)
Common stock held in treasury (in shares)	11,100,000	7,700,000
Series A Preferred Stock
Condensed Financial Statements, Captions [Line Items]
Preferred stock, stated value (in dollars per share)	$ 50	$ 50
Series B Preferred Stock
Condensed Financial Statements, Captions [Line Items]
Preferred stock, stated value (in dollars per share)	100	100
Parent Company
Condensed Financial Statements, Captions [Line Items]
Preferred stock, stated value (in dollars per share)	$ 0.20	$ 0.20
Preferred stock, shares authorized (in shares)	20,000,000	20,000,000
Common stock, par value (in dollars per share)	$ 0.20	$ 0.20
Common stock, shares authorized (in shares)	1,125,000,000	1,125,000,000
Common stock, shares issued (in shares)	443,500,000	436,600,000
Accumulated other comprehensive loss tax benefit	$ 1,696	$ (5,364)
Common stock held in treasury (in shares)	11,100,000	7,700,000
Parent Company | Series A Preferred Stock
Condensed Financial Statements, Captions [Line Items]
Preferred stock, stated value (in dollars per share)	$ 0	$ 50
Preferred stock, shares issued (in shares)	0	3,300,000
Parent Company | Series B Preferred Stock
Condensed Financial Statements, Captions [Line Items]
Preferred stock, stated value (in dollars per share)	$ 100	$ 100
Preferred stock, shares issued (in shares)	4,000,000	4,000,000