Consolidated Statements Of Cash Flows $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Statement of Cash Flows [Abstract]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 1,520	$ 1,363	$ 1,282
Interest Paid, Including Capitalized Interest, Operating and Investing Activities	1,090	474	332
Operating activities:
Net income (loss)	129	771	623
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of premiums and discounts on mortgage-backed securities, net	331	378	400
Amortization of accumulated other comprehensive loss on interest rate swaps de-designated as qualifying hedges	0	0	39
Amortization of intangible assets	25	3	2
Stock based compensation	6	4	1
(Gain) loss on sale of investment securities, net	137	63	(109)
Unrealized loss on investment securities measured at fair value through net income, net	297	71	6
(Gain) loss on derivative instruments and other securities, net	167	(193)	310
(Increase) decrease in other assets	(100)	82	34
Increase in accounts payable and other accrued liabilities	121	81	46
Net cash provided by operating activities	1,113	1,260	1,352
Investing activities:
Purchases of Agency mortgage-backed securities	(42,586)	(35,920)	(20,836)
Purchases of credit risk transfer and non-Agency securities	(1,572)	(1,074)	(229)
Proceeds from sale of Agency mortgage-backed securities	8,132	18,701	18,030
Proceeds from sale of credit risk transfer and non-Agency securities	891	494	0
Principal collections on Agency mortgage-backed securities	7,170	6,869	8,114
Principal collections on credit risk transfer and non-Agency securities	15	5	23
Payments on U.S. Treasury securities	(10,829)	(11,756)	(4,483)
Proceeds from U.S. Treasury securities	21,308	14,557	10,393
Net payments on reverse repurchase agreements	(10,571)	(3,162)	(6,003)
Net proceeds from (payments on) derivative instruments	76	253	(1,292)
Purchase of AGNC Mortgage Management, LLC, net of cash acquired	0	0	(555)
Net proceeds from (payments on) other investing activity	30	(28)	39
Net cash (used in) provided by investing activities	(27,936)	(11,061)	3,201
Financing activities:
Proceeds from repurchase arrangements	2,031,463	483,516	217,538
Payments on repurchase agreements	(2,006,042)	(471,078)	(221,434)
Proceeds from Federal Home Loan Bank advances	0	0	2,098
Payments on Federal Home Loan Bank advances	0	(3,037)	(2,814)
Payments on debt of consolidated variable interest entities	(78)	(104)	(135)
Net proceeds from preferred stock issuance	0	315	0
Payment for preferred stock redemption	0	(173)	0
Net proceeds from common stock issuances	2,611	1,238	0
Payment for common stock repurchases	0	0	(116)
Cash dividends paid	(974)	(795)	(799)
Net cash (used in) provided by financing activities	26,980	9,882	(5,662)
Net change in cash and cash equivalents	157	81	$ (1,109)
Cash and cash equivalents at end of period	$ 921	$ 1,046