Available-for-Sale (AFS) Securities (Summary of Securities with Unrealized Losses) (Details) (USD $)	Sep. 30, 2012		Dec. 31, 2011
Fair Value:
Less than 12 Months	$ 1,256,518,000		$ 1,079,594,000
Greater than 12 Months	778,237,000		1,303,661,000
Fair Value	2,034,755,000		2,383,255,000
Unrealized Losses:
Less than 12 Months	(1,296,000)		(12,096,000)
Greater than 12 Months	(45,114,000)		(161,156,000)
Unrealized Losses	(46,410,000)	[1]	(173,252,000)
Total Non-MBS [Member]
Fair Value:
Less than 12 Months	962,376,000
Greater than 12 Months	0
Fair Value	962,376,000
Unrealized Losses:
Less than 12 Months	(560,000)
Greater than 12 Months	0
Unrealized Losses	(560,000)	[1]
GSE securities [Member]
Fair Value:
Less than 12 Months	949,404,000
Greater than 12 Months	0.000000
Fair Value	949,404,000
Unrealized Losses:
Less than 12 Months	(537,000)
Greater than 12 Months	0.000000
Unrealized Losses	(537,000)	[1]
State and local agency obligations [Member]
Fair Value:
Less than 12 Months	12,972,000
Greater than 12 Months	0
Fair Value	12,972,000
Unrealized Losses:
Less than 12 Months	(23,000)
Greater than 12 Months	0
Unrealized Losses	(23,000)	[1]
Total MBS [Member]
Fair Value:
Less than 12 Months	294,142,000		1,079,594,000
Greater than 12 Months	778,237,000		1,303,661,000
Fair Value	1,072,379,000		2,383,255,000
Unrealized Losses:
Less than 12 Months	(736,000)		(12,096,000)
Greater than 12 Months	(45,114,000)		(161,156,000)
Unrealized Losses	(45,850,000)	[1]	(173,252,000)
Other US obligations MBS [Member]
Fair Value:
Less than 12 Months	249,725,000
Greater than 12 Months	0
Fair Value	249,725,000
Unrealized Losses:
Less than 12 Months	(204,000)
Greater than 12 Months	0
Unrealized Losses	(204,000)	[1]
GSE residential MBS [Member]
Fair Value:
Less than 12 Months	33,777,000		844,628,000
Greater than 12 Months	37,758,000		0
Fair Value	71,535,000		844,628,000
Unrealized Losses:
Less than 12 Months	(60,000)		(901,000)
Greater than 12 Months	(34,000)		0
Unrealized Losses	(94,000)	[1]	(901,000)
Private label MBS [Member]
Fair Value:
Less than 12 Months	10,640,000		234,966,000
Greater than 12 Months	740,479,000		1,303,661,000
Fair Value	751,119,000		1,538,627,000
Unrealized Losses:
Less than 12 Months	(472,000)		(11,195,000)
Greater than 12 Months	(45,080,000)		(161,156,000)
Unrealized Losses	(45,552,000)	[1]	(172,351,000)
Private label residential MBS [Member]
Fair Value:
Less than 12 Months	10,640,000		232,848,000
Greater than 12 Months	731,071,000		1,290,706,000
Fair Value	741,711,000		1,523,554,000
Unrealized Losses:
Less than 12 Months	(472,000)		(11,150,000)
Greater than 12 Months	(44,140,000)		(158,059,000)
Unrealized Losses	(44,612,000)	[1]	(169,209,000)
HELOCs [Member]
Fair Value:
Less than 12 Months	0		2,118,000
Greater than 12 Months	9,408,000		12,955,000
Fair Value	9,408,000		15,073,000
Unrealized Losses:
Less than 12 Months	0		(45,000)
Greater than 12 Months	(940,000)		(3,097,000)
Unrealized Losses	$ (940,000)	[1]	$ (3,142,000)

[1] Total unrealized losses equal the sum of "OTTI Recognized in AOCI" and "Gross Unrealized Losses" in the first two tables of this Note 4.