Equity Equity (Preferred Stock Dividends) (Details) - USD ($) $ / shares in Units, $ in Millions					3 Months Ended		6 Months Ended
	Mar. 05, 2020	Feb. 18, 2020	Mar. 05, 2019	Feb. 15, 2019	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Preferred Stock
Dividends Payable [Line Items]
Dividends Payable, Date Declared	Mar. 05, 2020	Feb. 18, 2020	Mar. 05, 2019	Feb. 15, 2019	May 15, 2020	May 15, 2019
Dividends Payable, Date of Record	Mar. 01, 2020	Feb. 29, 2020	Feb. 28, 2019	Feb. 28, 2019	May 29, 2020	May 31, 2019
Dividends Payable, Date to be Paid	Mar. 16, 2020	Mar. 16, 2020	Mar. 15, 2019	Mar. 15, 2019	Jun. 15, 2020	Jun. 17, 2019
Series A Preferred Stock
Dividends Payable [Line Items]
Preferred Stock, Dividends Per Share, Declared	$ 0.253	$ 0	$ 0.250	$ 0	$ 0.253	$ 0.261	$ 0.506	$ 0.511
Dividends, Preferred Stock, Cash	$ 6	$ 0	$ 6	$ 0	$ 6	$ 6	$ 12	$ 12
Series C Preferred Stock
Dividends Payable [Line Items]
Preferred Stock, Dividends Per Share, Declared	$ 0	$ 0	$ 0	$ 0	$ 26.250	$ 26.250	$ 26.250	$ 26.250
Dividends, Preferred Stock, Cash	$ 0	$ 0	$ 0	$ 0	$ 39	$ 39	$ 39	$ 39
Series D Preferred Stock
Dividends Payable [Line Items]
Preferred Stock, Dividends Per Share, Declared	$ 0	$ 29.375	$ 0	$ 29.375	$ 0	$ 0	$ 29.375	$ 29.375
Dividends, Preferred Stock, Cash	$ 0	$ 15	$ 0	$ 15	$ 0	$ 0	$ 15	$ 15
Series E Preferred Stock
Dividends Payable [Line Items]
Preferred Stock, Dividends Per Share, Declared	$ 0	$ 351.563	$ 0	$ 351.563	$ 351.563	$ 351.563	$ 703.126	$ 703.126
Dividends, Preferred Stock, Cash	$ 0	$ 11	$ 0	$ 11	$ 12	$ 12	$ 23	$ 23
Series F Preferred Stock [Member]
Dividends Payable [Line Items]
Preferred Stock, Dividends Per Share, Declared	$ 0	$ 0	$ 0	$ 0	$ 494.792	$ 0	$ 494.792	$ 0
Dividends, Preferred Stock, Cash	$ 0	$ 0	$ 0	$ 0	$ 20	$ 0	$ 20	$ 0