Available-for-Sale (AFS) Securities (Summary of Available-for-Sale Securities) (Details) (USD $)	Sep. 30, 2012		Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 6,297,647,000		$ 4,518,370,000
OTTI Recognized in AOCI	(45,130,000)	[1]	(168,171,000)	[1]
Gross Unrealized Gains	74,925,000		11,029,000
Gross Unrealized Losses	(1,280,000)		(5,081,000)
Fair Value	6,326,162,000		4,356,147,000
Total Non-MBS [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,410,900,000	[2]	901,993,000
OTTI Recognized in AOCI	0	[1]	0	[1]
Gross Unrealized Gains	234,000		579,000
Gross Unrealized Losses	(560,000)		0
Fair Value	1,410,574,000		902,572,000
Mutual Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,993,000	[2]	1,993,000	[2]
OTTI Recognized in AOCI	0	[1]	0	[1]
Gross Unrealized Gains	5,000		5,000
Gross Unrealized Losses	0		0
Fair Value	1,998,000		1,998,000
Other U.S. obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	21,000,000	[2]
OTTI Recognized in AOCI	0	[1]
Gross Unrealized Gains	20,000
Gross Unrealized Losses	0
Fair Value	21,020,000
GSE securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,374,912,000	[2]	900,000,000	[2]
OTTI Recognized in AOCI	0	[1]	0	[1]
Gross Unrealized Gains	209,000		574,000
Gross Unrealized Losses	(537,000)		0
Fair Value	1,374,584,000		900,574,000
State and local agency obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	12,995,000
OTTI Recognized in AOCI	0	[1]
Gross Unrealized Gains	0
Gross Unrealized Losses	(23,000)
Fair Value	12,972,000
Other US obligations MBS [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	326,160,000	[2]
OTTI Recognized in AOCI	0	[1]
Gross Unrealized Gains	85,000
Gross Unrealized Losses	(204,000)
Fair Value	326,041,000
Total MBS [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,886,747,000		3,616,377,000
OTTI Recognized in AOCI	(45,130,000)	[1]	(168,171,000)	[1]
Gross Unrealized Gains	74,691,000		10,450,000
Gross Unrealized Losses	(720,000)		(5,081,000)
Fair Value	4,915,588,000		3,453,575,000
GSE residential MBS [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,071,757,000		1,801,193,000	[2]
OTTI Recognized in AOCI	0	[1]	0	[1]
Gross Unrealized Gains	36,645,000		6,849,000
Gross Unrealized Losses	(94,000)		(901,000)
Fair Value	3,108,308,000		1,807,141,000
Private label MBS [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,488,830,000	[2]	1,815,184,000	[2]
OTTI Recognized in AOCI	(45,130,000)	[1]	(168,171,000)	[1]
Gross Unrealized Gains	37,961,000		3,601,000
Gross Unrealized Losses	(422,000)		(4,180,000)
Fair Value	1,481,239,000		1,646,434,000
Private label residential MBS [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,473,486,000	[2]	1,796,969,000	[2]
OTTI Recognized in AOCI	(44,190,000)	[1]	(165,029,000)	[1]
Gross Unrealized Gains	37,790,000		3,601,000
Gross Unrealized Losses	(422,000)		(4,180,000)
Fair Value	1,466,664,000		1,631,361,000
HELOCs [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	15,344,000	[2]	18,215,000	[2]
OTTI Recognized in AOCI	(940,000)	[1]	(3,142,000)	[1]
Gross Unrealized Gains	171,000		0
Gross Unrealized Losses	0		0
Fair Value	$ 14,575,000		$ 15,073,000

[1] Represents the noncredit portion of an OTTI recognized during the life of the security.

[2] Amortized cost includes adjustments made to the cost basis of an investment for accretion and/or amortization, collection of cash, and/or previous OTTI recognized in earnings.