Consolidated Statements Of Comprehensive Income - USD ($) 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
Dividends declared per common share	$ 0.54	$ 0.54	$ 0.54	$ 0.54	$ 0.54	$ 0.54	$ 0.54	$ 0.54
Interest income:
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
Other gain (loss), net:
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)
Gain (loss) 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
Total other gain (loss), net:	(971)	73	134	217	194	126	(141)	(104)	(547)	75	(199)
Expenses:
Management fee expense									0	0	52
Compensation and benefits	11	14	10	10	12	10	10	10	45	42	19
Other operating expense	8	31	8	8	9	8	6	8	55	31	34
Total operating expense	19	45	18	18	21	18	16	18	100	73	105
Net income	(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
Issuance costs of redeemed preferred stock					0	6	0	0	0	6	0
Net income available to common stockholders	(813)	207	284	415	376	271	17	69	93	733	595
Other comprehensive income (loss):
Unrealized gain (loss) on available-for-sale securities, net	(361)	193	145	621	205	(90)	(121)	(46)	598	(52)	370
Unrealized gain on derivative instruments, net									0	0	39
Other comprehensive income (loss)									(598)	52	(331)
Comprehensive income (loss)	(443)	23	148	(197)	180	376	145	122	(469)	823	292
Comprehensive income (loss) available (attributable) to common stockholders	$ (452)	$ 14	$ 139	$ (206)	$ 171	$ 361	$ 138	$ 115	$ (505)	$ 785	$ 264
Weighted average number of common 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
Weighted average number of common 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
Net income per common share - basic	$ (1.61)	$ 0.45	$ 0.70	$ 1.06	$ 0.96	$ 0.74	$ 0.05	$ 0.21	$ 0.21	$ 2.04	$ 1.79
Net income per common share - diluted									$ 0.21	$ 2.04	$ 1.79