Held-to-Maturity (HTM) Securities (Summary of Held-to-Maturity Securities) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 6,335,836	$ 8,832,845
Gross Unrealized Holding Gains	141,584	103,376
Gross Unrealized Holding Losses	(61,350)	(153,873)
Fair Value	6,416,070	8,782,348
Certificates of Deposit [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	700,000	2,000,000
Gross Unrealized Holding Gains	60	180
Gross Unrealized Holding Losses	0	0
Fair Value	700,060	2,000,180
GSE securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	27,842	38,589
Gross Unrealized Holding Gains	1,386	1,860
Gross Unrealized Holding Losses	0	0
Fair Value	29,228	40,449
State and local agency obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	261,597	278,704
Gross Unrealized Holding Gains	8,215	2,668
Gross Unrealized Holding Losses	(19,022)	(34,291)
Fair Value	250,790	247,081
Held To Maturity Securities Other Than Mortgage Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	989,439	2,317,293
Gross Unrealized Holding Gains	9,661	4,708
Gross Unrealized Holding Losses	(19,022)	(34,291)
Fair Value	980,078	2,287,710
Other US obligations MBS [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,057,614	2,411,090
Gross Unrealized Holding Gains	14,224	11,273
Gross Unrealized Holding Losses	0	(91)
Fair Value	2,071,838	2,422,272
GSE residential MBS [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	1,979,170	2,462,698
Gross Unrealized Holding Gains	106,908	83,222
Gross Unrealized Holding Losses	(440)	(1,939)
Fair Value	2,085,638	2,543,981
Private Label Residential MBS [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	1,296,689	1,624,190
Gross Unrealized Holding Gains	10,791	4,173
Gross Unrealized Holding Losses	(39,551)	(113,072)
Fair Value	1,267,929	1,515,291
HELOCs [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	12,924	17,574
Gross Unrealized Holding Gains	0	0
Gross Unrealized Holding Losses	(2,337)	(4,480)
Fair Value	10,587	13,094
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	1,309,613	1,641,764
Gross Unrealized Holding Gains	10,791	4,173
Gross Unrealized Holding Losses	(41,888)	(117,552)
Fair Value	1,278,516	1,528,385
MBS [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	5,346,397	6,515,552
Gross Unrealized Holding Gains	131,923	98,668
Gross Unrealized Holding Losses	(42,328)	(119,582)
Fair Value	$ 5,435,992	$ 6,494,638