Schedule of Net Income (Loss) Per Share Reconciliation (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net Income Per Common Share:
Net income (loss) attributable to Annaly	$ (658,272)	$ 354,856	$ (335,512)	$ (203,351)	$ 1,028,749	$ 192,458	$ 1,638,213	$ 870,278	$ (842,083)	$ 3,729,698	$ 1,735,900
Less: Preferred stock dividends	17,992	17,992	17,992	17,992	17,992	17,992	17,992	17,992	71,968	71,968	39,530
Net income (loss) per share available (related) to common stockholders, prior to adjustment for dilutive potential common shares, if necessary	(676,068)	336,864	(353,504)	(221,343)	1,010,757	174,466	1,620,221	852,286	(914,051)	3,657,730	1,696,370
Add: Interest on Convertible Senior Notes, if dilutive										67,056	27,843
Net income (loss) available to common stockholders, as adjusted									(914,051)	3,724,786	1,724,213
Weighted average shares of common stock outstanding-basic									947,539,294	947,337,915	972,902,459
Add: Effect of stock awards and Convertible Senior Notes, if dilutive										48,219,111	32,852,598
Weighted average shares of common stock outstanding-diluted									947,539,294	995,557,026	1,005,755,057
Net income (loss) per share available (related) to common share:
Basic	$ (0.71)	$ 0.36	$ (0.37)	$ (0.23)	$ 1.07	$ 0.18	$ 1.71	$ 0.90	$ (0.96)	$ 3.86	$ 1.74
Diluted	$ (0.71)	$ 0.35	$ (0.37)	$ (0.23)	$ 1.03	$ 0.18	$ 1.64	$ 0.87	$ (0.96)	$ 3.74	$ 1.71
Parent
Net Income Per Common Share:
Net income (loss) attributable to Annaly									$ (842,083)	$ 3,729,698	$ 1,735,900