Equity Equity (Preferred Stock Dividends) (Details) - USD ($) $ / shares in Units, $ in Millions			3 Months Ended
	Mar. 05, 2019	Feb. 15, 2019	Mar. 31, 2019	Mar. 31, 2018
Preferred Stock
Dividends Payable [Line Items]
Dividends Payable, Date Declared	Mar. 05, 2019	Feb. 15, 2019		Mar. 05, 2018
Dividends Payable, Date of Record	Feb. 28, 2019	Feb. 28, 2019		Feb. 28, 2018
Dividends Payable, Date to be Paid	Mar. 15, 2019	Mar. 15, 2019		Mar. 15, 2018
Series A Preferred Stock
Dividends Payable [Line Items]
Preferred Stock, Dividends Per Share, Declared	$ 0.250	$ 0.000	$ 0.250	$ 0.250
Dividends, Preferred Stock, Cash	$ 6	$ 0	$ 6	$ 6
Series C Preferred Stock
Dividends Payable [Line Items]
Preferred Stock, Dividends Per Share, Declared	$ 0.000	$ 0.000	$ 0.000	$ 0.000
Dividends, Preferred Stock, Cash	$ 0	$ 0	$ 0	$ 0
Series D Preferred Stock
Dividends Payable [Line Items]
Preferred Stock, Dividends Per Share, Declared	$ 0.000	$ 29.375	$ 29.375	$ 0.000
Dividends, Preferred Stock, Cash	$ 0	$ 15	$ 15	$ 0
Series E Preferred Stock
Dividends Payable [Line Items]
Preferred Stock, Dividends Per Share, Declared	$ 0.000	$ 351.563	$ 351.563	$ 0.000
Dividends, Preferred Stock, Cash	$ 0	$ 11	$ 11	$ 0