Equity (Preferred Stock) (Details) - USD ($)				1 Months Ended	3 Months Ended												12 Months Ended
	Dec. 01, 2019	Aug. 31, 2019	Mar. 05, 2019	Mar. 31, 2018	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jun. 04, 2018	Mar. 20, 2018
Dividends Payable [Line Items]
Preferred Stock, Shares Authorized					200,000,000				200,000,000								200,000,000	200,000,000
Preferred Stock, Shares Issued					26,032,200				26,032,200								26,032,200	26,032,200
Preferred Stock, Shares Outstanding					26,032,200				26,032,200								26,032,200	26,032,200
Preferred Stock [Member]
Preferred Stock
Declaration Date			Mar. 05, 2019		Nov. 15, 2019	Aug. 15, 2019	May 15, 2019	Feb. 15, 2019	Nov. 15, 2018	Aug. 15, 2018	May 15, 2018	Mar. 05, 2018	Nov. 15, 2017	Aug. 15, 2017	May 15, 2017	Mar. 06, 2017
Record Date	Dec. 01, 2019	Aug. 31, 2019			Nov. 30, 2019	Sep. 01, 2019	May 31, 2019	Feb. 28, 2019	Nov. 30, 2018	Aug. 31, 2018	May 31, 2018	Feb. 28, 2018	Nov. 30, 2017	Aug. 31, 2017	May 31, 2017	Feb. 28, 2017
Payment Date					Dec. 16, 2019	Sep. 16, 2019	Jun. 17, 2019	Mar. 15, 2019	Dec. 17, 2018	Sep. 17, 2018	Jun. 15, 2018	Mar. 15, 2018	Dec. 15, 2017	Sep. 15, 2017	Jun. 15, 2017	Mar. 15, 2017
Series A Preferred Stock [Member]
Dividends Payable [Line Items]
Preferred Stock, Dividend Payment Rate, Variable																	Three-month LIBOR + 1.00%, with floor of 4.00%
Preferred Stock, Shares Authorized					27,600,000				27,600,000								27,600,000	27,600,000
Preferred Stock, Shares Issued					24,000,000				24,000,000								24,000,000	24,000,000
Preferred Stock, Shares Outstanding					24,000,000				24,000,000								24,000,000	24,000,000
Preferred Stock
Preferred Stock, Dividends Per Share, Declared	$ 0.253	$ 0	$ 0.250		$ 0	$ 0.253	$ 0.261	$ 0	$ 0.253	$ 0.256	$ 0.256	$ 0.250	$ 0.253	$ 0.256	$ 0.256	$ 0.250	$ 1.017	$ 1.015	$ 1.015
Preferred stock, dividends	$ 6,000,000	$ 0	$ 6,000,000		$ 0	$ 6,000,000	$ 6,000,000	$ 0	$ 6,000,000	$ 6,000,000	$ 7,000,000	$ 6,000,000	$ 6,000,000	$ 6,000,000	$ 7,000,000	$ 6,000,000	$ 24,000,000	$ 25,000,000	$ 25,000,000
Series C Preferred Stock [Member]
Dividends Payable [Line Items]
Preferred Stock, Dividend Payment Rate, Variable																	5.25% Fixed-to-Floating Rate
Preferred Stock, Shares Authorized					1,500,000				1,500,000								1,500,000	1,500,000
Preferred Stock, Shares Issued					1,500,000				1,500,000								1,500,000	1,500,000
Preferred Stock, Shares Outstanding					1,500,000				1,500,000								1,500,000	1,500,000
Preferred Stock
Preferred Stock, Dividends Per Share, Declared	$ 0	$ 0	$ 0		$ 26.250	$ 0	$ 26.250	$ 0	$ 26.250	$ 0	$ 26.250	$ 0	$ 26.250	$ 0	$ 26.250	$ 0	$ 52.500	$ 52.500	$ 52.500
Preferred stock, dividends	$ 0	$ 0	$ 0		$ 40,000,000	$ 0	$ 39,000,000	$ 0	$ 40,000,000	$ 0	$ 39,000,000	$ 0	$ 39,000,000	$ 0	$ 39,000,000	$ 0	$ 79,000,000	$ 79,000,000	$ 78,000,000
Series D Preferred Stock [Member]
Dividends Payable [Line Items]
Preferred Stock, Dividend Payment Rate, Variable				5.875% Fixed-to-Floating Rate
Preferred Stock, Shares Authorized					500,000				500,000								500,000	500,000
Preferred Stock, Shares Issued					500,000				500,000								500,000	500,000			500,000
Preferred Stock, Shares Outstanding					500,000				500,000								500,000	500,000
Preferred Stock
Preferred Stock, Dividends Per Share, Declared	$ 0	$ 29.375	$ 0		$ 0	$ 0	$ 0	$ 29.375	$ 0	$ 28.233	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 58.750	$ 28.233	$ 0
Preferred stock, dividends	$ 0	$ 15,000,000	$ 0		$ 0	$ 0	$ 0	$ 15,000,000	$ 0	$ 14,000,000	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 30,000,000	$ 14,000,000	$ 0
Series E Preferred Stock [Member]
Dividends Payable [Line Items]
Preferred Stock, Shares Authorized					32,200				32,200								32,200	32,200
Preferred Stock, Shares Issued					32,200				32,200								32,200	32,200		32,200
Preferred Stock, Shares Outstanding					32,200				32,200								32,200	32,200
Preferred Stock
Preferred Stock, Dividends Per Share, Declared	$ 0	$ 351.563	$ 0		$ 351.563	$ 0	$ 351.563	$ 351.563	$ 351.563	$ 394.531	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 1,406.252	$ 746.094	$ 0
Preferred stock, dividends	$ 0	$ 11,000,000	$ 0		$ 11,000,000	$ 0	$ 12,000,000	$ 11,000,000	$ 11,000,000	$ 12,000,000	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 45,000,000	$ 23,000,000	$ 0
Series A Junior Preferred Stock [Member]
Dividends Payable [Line Items]
Preferred Stock, Shares Authorized					10,000,000				10,000,000								10,000,000	10,000,000
Preferred Stock, Shares Issued					0				0								0	0
Preferred Stock, Shares Outstanding					0				0								0	0
Not Designated Preferred Stock [Member]
Dividends Payable [Line Items]
Preferred Stock, Shares Authorized					160,367,800				160,367,800								160,367,800	160,367,800
Preferred Stock, Shares Issued					0				0								0	0
Preferred Stock, Shares Outstanding					0				0								0	0