Capital Stock (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jun. 29, 2018	Jul. 10, 2017
Class of Stock [Line Items]
Common Stock, Shares Authorized	175,000,000	175,000,000			175,000,000
Preferred Stock, Shares Authorized	50,000,000	50,000,000
Common stock, par value (in dollars per share)	$ 0.25	$ 0.25
Proceeds from Issuance of Common Stock			$ 799
Preferred Stock, Dividend Rate, Percentage	11.125%	11.125%
Preferred Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Proceeds from Issuance of Preferred Stock and Preference Stock			1,866
Preferred dividends	$ 214	$ 214	$ 120
Scenario, Previously Reported [Member]
Class of Stock [Line Items]
Common Stock, Shares Authorized		1,750,000,000
Common Stock [Member]
Class of Stock [Line Items]
Common stock, par value (in dollars per share)	$ 0.25
Common Stock [Member] | Scenario, Previously Reported [Member]
Class of Stock [Line Items]
Stock Issued During Period Shares Excluding Over Allotment New Issues			150,000,000
Shares Issued, Price Per Share	$ 5
Over Allotment Option Shares Issued	15,000,000
Preferred Stock [Member]
Class of Stock [Line Items]
Stock Issued During Period Shares Excluding Over Allotment New Issues	17,500,000
Shares Issued, Price Per Share	$ 100
Over Allotment Option Shares Issued	1,750,000
Preferred Stock, Dividend Rate, Percentage	11.125%
Preferred Stock, Par or Stated Value Per Share	$ 0.01
Preferred Stock, Liquidation Preference Per Share	$ 100.00
Restricted cash			$ 1,955
Proceeds from Equity, Net of Issuance Costs			$ 2,665
Minimum [Member] | Preferred Stock [Member] | Scenario, Forecast [Member]
Class of Stock [Line Items]
Convertible Preferred Stock, Shares Issued upon Conversion				1.1348
Maximum [Member] | Preferred Stock [Member] | Scenario, Forecast [Member]
Class of Stock [Line Items]
Convertible Preferred Stock, Shares Issued upon Conversion				1.3333