Stockholders' Equity (Tables)
 6 Months Ended 12 Months Ended
Jun. 30, 2016
Dec. 31, 2015
Stockholders' Equity Note [Abstract]    
Schedule of Stock by Class
Preferred stock with a par value of $0.01 and a liquidation value of $1,000 and additional paid in capital attributable to preferred stock at June 30, 2016 is summarized as follows: 
 
Rate
 
Earliest
Redemption Date
 
Shares
Outstanding
 
Preferred
Shares
 
 
 
 
 
 
 
(Dollars in millions)
Series C Preferred Stock
9.0
%
 
1/31/2012
 
266,657

 
$
267
Preferred stock with a par value of $0.01 and a liquidation value of $1,000 and additional paid in capital attributable to preferred stock at December 31, 2015 is summarized as follows. 
 
Dividend Rate (1)
 
Earliest Redemption Date (1)
 
Shares
Outstanding
 
Preferred
Shares
 
Preferred Stock
 
(Dollars in millions)
Series C Preferred Stock
9.0
%
 
1/31/2012
 
266,657

 
$
—

 
$
267


(1)
Earliest redemption date at the Company's option.