Securities - Summary of Portfolio of Securities Held to Maturity (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 7,277,102	[1]	$ 7,679,472	[2]
Carrying Amount	7,268,244	[1]	7,670,282	[2]
Gross Unrealized Gain	164,686	[1]	80,203	[2]
Gross Unrealized Loss	115,915	[1]	305,241	[2]
Fair Value	7,317,015	[1]	7,445,244	[2]
Mortgage-Related Securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	4,279,814		4,407,987
Carrying Amount	4,279,814		4,407,987
Gross Unrealized Gain	130,183		59,475
Gross Unrealized Loss	17,244		83,800
Fair Value	4,392,753		4,383,662
Mortgage-Related Securities | GSE certificates
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,515,030		2,529,102
Carrying Amount	2,515,030		2,529,102
Gross Unrealized Gain	74,212		30,145
Gross Unrealized Loss	13,892		61,280
Fair Value	2,575,350		2,497,967
Mortgage-Related Securities | GSE CMOs
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	1,764,784		1,878,885
Carrying Amount	1,764,784		1,878,885
Gross Unrealized Gain	55,971		29,330
Gross Unrealized Loss	3,352		22,520
Fair Value	1,817,403		1,885,695
Other Securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,997,288		3,271,485
Carrying Amount	2,988,430		3,262,295
Gross Unrealized Gain	34,503		20,728
Gross Unrealized Loss	98,671		221,441
Fair Value	2,924,262		3,061,582
Other Securities | GSE debentures
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,780,330		3,053,253
Carrying Amount	2,780,330		3,053,253
Gross Unrealized Gain	16,530		6,512
Gross Unrealized Loss	86,860		208,506
Fair Value	2,710,000		2,851,259
Other Securities | Corporate bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	73,211		72,899
Carrying Amount	73,211		72,899
Gross Unrealized Gain	12,381		11,063
Fair Value	85,592		83,962
Other Securities | Municipal bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	59,277		60,462
Carrying Amount	59,277		60,462
Gross Unrealized Gain	5		19
Gross Unrealized Loss	1,775		3,849
Fair Value	57,507		56,632
Other Securities | Capital trust notes
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	84,470		84,871
Carrying Amount	75,612		75,681
Gross Unrealized Gain	5,587		3,134
Gross Unrealized Loss	10,036		9,086
Fair Value	$ 71,163		$ 69,729

[1] Held-to-maturity securities are reported at a carrying amount equal to amortized cost less the non-credit portion of OTTI recorded in AOCL. At September 30, 2014, the non-credit portion of OTTI recorded in AOCL was $8.9 million (before taxes).

[2] Held-to-maturity securities are reported at a carrying amount equal to amortized cost less the non-credit portion of OTTI recorded in AOCL. At December 31, 2013, the non-credit portion of OTTI recorded in AOCL was $9.2 million (before taxes).