Capital Stock (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2015
Class of Stock [Line Items]
Class of stock conversion, rate	1.3333
Dividends payable	$ 54
Common Stock [Member]
Class of Stock [Line Items]
Shares issued in stock conversion	25,529,000
Preferred Stock [Member]
Class of Stock [Line Items]
Stock Issued During Period Shares Excluding Over Allotment New Issues		17,500,000
Preferred Stock, Dividend Rate, Percentage	11.125%
Preferred Stock, Par or Stated Value Per Share	$ 0.01
Shares Issued, Price Per Share		$ 100
Over Allotment Option Shares Issued		1,750,000