Capital Preferred Stock (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Class of Stock [Line Items]
Preferred Stock, Shares Outstanding	25,000	12,000
Preferred Stock, Value, Outstanding	$ 2,475	$ 1,225	$ 1,225
Series A Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Outstanding	1,725
Preferred Stock, Value, Outstanding	$ 172	172	172
Series B Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Outstanding	1,025
Preferred Stock, Value, Outstanding	$ 103	103	103
Series E Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Outstanding	4,500
Preferred Stock, Value, Outstanding	$ 450	450	450
Series F Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Outstanding	5,000
Preferred Stock, Value, Outstanding	$ 500	$ 500	$ 500
Series G Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Outstanding	7,500
Preferred Stock, Value, Outstanding	$ 750
Series H Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Outstanding	5,000
Preferred Stock, Value, Outstanding	$ 500