Equity Equity (Preferred Stock Dividends) (Details) - USD ($) $ / shares in Units, $ in Millions			3 Months Ended			6 Months Ended
	Mar. 05, 2019	Feb. 15, 2019	Jun. 30, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Preferred Stock
Dividends Payable [Line Items]
Dividends Payable, Date Declared	Mar. 05, 2019	Feb. 15, 2019	May 15, 2019	May 15, 2018	Mar. 05, 2018
Dividends Payable, Date of Record	Feb. 28, 2019	Feb. 28, 2019	May 31, 2019	May 31, 2018	Feb. 28, 2018
Dividends Payable, Date to be Paid	Mar. 15, 2019	Mar. 15, 2019	Jun. 17, 2019	Jun. 15, 2018	Mar. 15, 2018
Series A Preferred Stock
Dividends Payable [Line Items]
Preferred Stock, Dividends Per Share, Declared	$ 0.250	$ 0	$ 0.261	$ 0.256	$ 0.250	$ 0.511	$ 0.506
Dividends, Preferred Stock, Cash	$ 6	$ 0	$ 6	$ 7	$ 6	$ 12	$ 13
Series C Preferred Stock
Dividends Payable [Line Items]
Preferred Stock, Dividends Per Share, Declared	$ 0	$ 0	$ 26.250	$ 26.250	$ 0	$ 26.250	$ 26.250
Dividends, Preferred Stock, Cash	$ 0	$ 0	$ 39	$ 39	$ 0	$ 39	$ 39
Series D Preferred Stock
Dividends Payable [Line Items]
Preferred Stock, Dividends Per Share, Declared	$ 0	$ 29.375	$ 0	$ 0	$ 0	$ 29.375	$ 0
Dividends, Preferred Stock, Cash	$ 0	$ 15	$ 0	$ 0	$ 0	$ 15	$ 0
Series E Preferred Stock
Dividends Payable [Line Items]
Preferred Stock, Dividends Per Share, Declared	$ 0	$ 351.563	$ 351.563	$ 0	$ 0	$ 703.126	$ 0
Dividends, Preferred Stock, Cash	$ 0	$ 11	$ 12	$ 0	$ 0	$ 23	$ 0