Held-to-Maturity (HTM) Securities (Redemption Terms) (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
Held-to-maturity Securities, Fair Value	6,416,070	8,782,348
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
Held-to-maturity Securities, Fair Value	980,078	2,287,710
Amortized Cost:
Due in one year or less	701,740	2,000,000
Due after one year through five years	28,163	41,594
Due after five years through ten years	8,069	7,420
Due after ten years	251,467	268,279
Amortized Cost	989,439	2,317,293
Held-to-maturity Securities, Debt Maturities, Fair Value [Abstract]
Due in one year or less	701,817	2,000,180
Due after one year through five years	29,559	43,528
Due after five years through ten years	8,158	7,159
Due after ten years	240,544	236,843
Fair Value	980,078	2,287,710
MBS [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	5,346,397	6,515,552
Held-to-maturity Securities, Fair Value	$ 5,435,992	$ 6,494,638