Fair Value Disclosures Fair Value Option (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Fair Value, Option, Quantitative Disclosures [Roll Forward]
Balance at beginning of period	$ (3,402,366)	$ (4,900,296)
New transactions elected for fair value option	0	(1,115,000)
Maturities and terminations	1,400,000	1,810,000
Net losses on instruments held under the fair value option	532	2,621
Change in accrued interest	(234)	135
Balance at end of period	$ (2,002,068)	$ (4,202,540)