CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net interest income:
Interest income		$ 2,493,126	$ 2,210,951	$ 2,170,697
Interest expense		1,008,354	657,752	471,596
Net interest income		1,484,772	1,553,199	1,699,101
Realized and unrealized gains (losses):
Realized gains (losses) on interest rate swaps	[1]	(371,108)	(506,681)	(624,495)
Realized gains (losses) on termination of interest rate swaps		(160,133)	(113,941)	(226,462)
Unrealized gains (losses) on interest rate swaps		512,918	282,190	(124,869)
Subtotal		(18,323)	(338,432)	(975,826)
Net gains (losses) on disposal of investments		(3,938)	33,089	50,987
Net gains (losses) on trading assets		261,438	230,580	29,623
Net unrealized gains (losses) on investments measured at fair value through earnings		(39,684)	86,391	(103,169)
Bargain purchase gain		0	72,576	0
Impairment of goodwill		0	0	(22,966)
Subtotal		217,816	422,636	(45,525)
Total realized and unrealized gains (losses)		199,493	84,204	(1,021,351)
Other income (loss):
Investment advisory income		0	0	24,848
Dividend income from affiliate		0	0	8,636
Other income (loss)		115,857	44,144	(47,201)
Total other income (loss)		115,857	44,144	(13,717)
General and administrative expenses:
Compensation and management fee		164,322	151,599	150,286
Other general and administrative expenses		59,802	98,757	49,954
Total general and administrative expenses		224,124	250,356	200,240
Income (loss) before income taxes		1,575,998	1,431,191	463,793
Income taxes		6,982	(1,595)	(1,954)
Net income (loss)		1,569,016	1,432,786	465,747
Net income (loss) attributable to noncontrolling interest		(588)	(970)	(809)
Net income (loss) attributable to Annaly		1,569,604	1,433,756	466,556
Dividends on preferred stock		109,635	82,260	71,968
Net income (loss) available (related) to common stockholders		$ 1,459,969	$ 1,351,496	$ 394,588
Net income (loss) per share available (related) to common stockholders:
Basic (in dollars per share)		$ 1.37	$ 1.39	$ 0.42
Diluted (in dollars per share)		$ 1.37	$ 1.39	$ 0.42
Weighted average number of common shares outstanding:
Basic (in shares)		1,065,923,652	969,787,583	947,062,099
Diluted (in shares)		1,066,351,616	970,102,353	947,276,742
Net income (loss)		$ 1,569,016	$ 1,432,786	$ 465,747
Other comprehensive income (loss):
Unrealized gains (losses) on available-for-sale securities		(89,997)	(686,414)	(531,952)
Reclassification adjustment for net (gains) losses included in net income (loss)		49,870	(21,883)	(50,527)
Other comprehensive income (loss)		(40,127)	(708,297)	(582,479)
Comprehensive income (loss)		1,528,889	724,489	(116,732)
Comprehensive income (loss) attributable to noncontrolling interest		(588)	(970)	(809)
Comprehensive income (loss) attributable to Annaly		1,529,477	725,459	(115,923)
Dividends on preferred stock		109,635	82,260	71,968
Comprehensive income (loss) attributable to common stockholders		$ 1,419,842	$ 643,199	$ (187,891)

[1] Consists of interest expense on interest rate swaps.