Quarterly Results (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	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, 2018	Dec. 31, 2017	Dec. 31, 2016
Interest income	$ 604	$ 500	$ 414	$ 431	$ 386	$ 318	$ 293	$ 296	$ 1,949	$ 1,293	$ 1,321
Interest expense	418	312	237	206	174	140	112	98	1,173	524	394
Net interest income	186	188	177	225	212	178	181	198	776	769	927
Noninterest Income [Abstract]
Gain (loss) on sale of investment securities, net	(21)	(40)	(74)	(2)	(16)	22	15	(84)	(137)	(63)	109
Unrealized loss on investment securities measured at fair value through net income, net	683	(363)	(94)	(523)	(65)	(31)	9	16	(297)	(71)	(6)
(Loss) gain on derivative instruments and other securities, net	(1,633)	430	298	738	271	131	(169)	(40)	(167)	193	(310)
Management Fee Income	$ 0	$ 46	$ 4	$ 4	$ 4	$ 4	$ 4	$ 4	$ 54	$ 16	$ 8
Weighted Average Number of Shares Outstanding, Diluted	504.2	462.7	405.2	391.5	391.5	364.9	346.5	331.1	441.4	358.7	331.9
Earnings Per Share, Basic	$ (1.61)	$ 0.45	$ 0.70	$ 1.06	$ 0.96	$ 0.74	$ 0.05	$ 0.21	$ 0.21	$ 2.04	$ 1.79
Total other (loss) income, net	$ (971)	$ 73	$ 134	$ 217	$ 194	$ 126	$ (141)	$ (104)	$ (547)	$ 75	$ (199)
Management fees									0	0	52
Labor and Related Expense	11	14	10	10	12	10	10	10	45	42	19
General and administrative expenses	8	31	8	8	9	8	6	8	55	31	34
Total expenses	19	45	18	18	21	18	16	18	100	73	105
Net income (loss)	(804)	216	293	424	385	286	24	76	129	771	623
Dividend on preferred stock	9	9	9	9	9	9	7	7	36	32	28
Net income (loss) available (attributable) to common shareholders	(813)	207	284	415	376	271	17	69	93	733	595
Unrealized Gains and (Losses), Net	$ 361	$ (193)	$ (145)	$ (621)	(205)	90	121	46	(598)	52	(370)
Issuance costs of redeemed preferred stock					$ 0	$ 6	$ 0	$ 0	$ 0	$ 6	$ 0
Weighted Average Number of Shares Outstanding, Basic	504.2	462.3	404.9	391.3	391.3	364.7	346.4	331.0	441.1	358.6	331.9
Unrealized gain on derivative instruments, net									$ 0	$ 0	$ 39
Other comprehensive (loss) income									(598)	52	(331)
Comprehensive (loss) income	$ (443)	$ 23	$ 148	$ (197)	$ 180	$ 376	$ 145	$ 122	(469)	823	292
Comprehensive (loss) income (attributable) available to common shareholders	$ (452)	$ 14	$ 139	$ (206)	$ 171	$ 361	$ 138	$ 115	$ (505)	$ 785	$ 264
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Common Stock, Dividends, Per Share, Declared	$ 0.54	$ 0.54	$ 0.54	$ 0.54	$ 0.54	$ 0.54	$ 0.54	$ 0.54
Comprehensive income per share - basic and diluted	$ (0.90)	$ 0.03	$ 0.34	$ (0.53)	$ 0.44	$ 0.99	$ 0.40	$ 0.35