Consolidated Statement of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Series D Preferred Stock [Member]	Series F Preferred Stock [Member]	Series A Warrants [Member]	Preferred Stock [Member]	Preferred Stock [Member] Series D Preferred Stock [Member]	Preferred Stock [Member] Series F Preferred Stock [Member]	Common Stock [Member]	Common Stock [Member] Series A Warrants [Member]	Common Stock Issuable [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] Series F Preferred Stock [Member]	Additional Paid-in Capital [Member] Series A Warrants [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss), Net [Member]	Treasury Stock [Member]	Treasury Stock [Member] Series A Warrants [Member]
Beginning balance at Dec. 31, 2014	$ 12,335,896				$ 1,231,500			$ 66,157		$ 2,608	$ 3,409,506			$ 7,807,119	$ (180,994)
Total comprehensive income	1,009,034													1,079,667	(70,633)
Acquisition of Hudson City Bancorp, Inc, common stock issued	3,110,581							12,977			3,097,604
Acquisition of Hudson City Bancorp, Inc, common stock awards converted	28,243										28,243
Preferred stock cash dividends	(81,270)													(81,270)
Exercise of stock warrants into common stock									$ 1				$ (1)
Stock-based compensation plans:
Compensation expense, net	43,195							155			43,040
Exercises of stock options, net	88,893							438			88,455
Stock purchase plan	10,346							45			10,301
Directors’ stock plan	1,761							7			1,754
Deferred compensation plans, net, including dividend equivalents	(51)							2		(244)	293			(102)
Other	1,573										1,573
Common stock cash dividends - $2.80 per share	(374,912)													(374,912)
Ending balance at Dec. 31, 2015	16,173,289				1,231,500			79,782		2,364	6,680,768			8,430,502	(251,627)
Total comprehensive income	1,272,105													1,315,114	(43,009)
Preferred stock cash dividends	(81,270)													(81,270)
Redemption of Series D Preferred Stock		$ (500,000)				$ (500,000)
Issuance of preferred stock			$ 495,000				$ 500,000					$ (5,000)
Exercise of stock warrants into common stock				$ (2)									(4,750)				$ 4,748
Purchases of treasury stock	(641,334)															$ (641,334)
Stock-based compensation plans:
Compensation expense, net	27,290							169			16,132					10,989
Exercises of stock options, net	169,617							18			(12,190)					181,789
Stock purchase plan	10,594										275					10,319
Directors’ stock plan	2,080							2			535					1,543
Deferred compensation plans, net, including dividend equivalents	3							2		(219)	163			(93)		150
Other	1,015										1,015
Common stock cash dividends - $2.80 per share	(441,765)													(441,765)
Ending balance at Dec. 31, 2016	16,486,622				1,231,500			79,973		2,145	6,676,948			9,222,488	(294,636)	(431,796)
Total comprehensive income	1,403,157													1,408,306	(5,149)
Reclassification of income tax effects to retained earnings	(64,029)													64,029	(64,029)
Preferred stock cash dividends	(72,734)													(72,734)
Exercise of stock warrants into common stock													$ (28,746)				$ 28,746
Purchases of treasury stock	(1,205,905)															(1,205,905)
Stock-based compensation plans:
Compensation expense, net	12,004							(64)			(47,670)					59,738
Exercises of stock options, net	72,274										(12,142)					84,416
Stock purchase plan	10,831										2,563					8,268
Directors’ stock plan	1,926										270					1,656
Deferred compensation plans, net, including dividend equivalents	(156)									(298)	(368)			(85)		595
Common stock cash dividends - $2.80 per share	(457,200)													(457,200)
Ending balance at Dec. 31, 2017	$ 16,250,819				$ 1,231,500			$ 79,909		$ 1,847	$ 6,590,855			$ 10,164,804	$ (363,814)	$ (1,454,282)